[SPARK-4608][Streaming] Reorganize StreamingContext implicit to improve API convenience

There is only one implicit function `toPairDStreamFunctions` in `StreamingContext`. This PR did similar reorganization like [SPARK-4397](https://issues.apache.org/jira/browse/SPARK-4397).

Compiled the following codes with Spark Streaming 1.1.0 and ran it with this PR. Everything is fine.
```Scala
import org.apache.spark._
import org.apache.spark.streaming._
import org.apache.spark.streaming.StreamingContext._

object StreamingApp {

  def main(args: Array[String]) {
    val conf = new SparkConf().setMaster("local[2]").setAppName("FileWordCount")
    val ssc = new StreamingContext(conf, Seconds(10))
    val lines = ssc.textFileStream("/some/path")
    val words = lines.flatMap(_.split(" "))
    val pairs = words.map(word => (word, 1))
    val wordCounts = pairs.reduceByKey(_ + _)
    wordCounts.print()

    ssc.start()
    ssc.awaitTermination()
  }
}
```

Author: zsxwing <zsxwing@gmail.com>

Closes #3464 from zsxwing/SPARK-4608 and squashes the following commits:

aa6d44a [zsxwing] Fix a copy-paste error
f74c190 [zsxwing] Merge branch 'master' into SPARK-4608
e6f9cc9 [zsxwing] Update the docs
27833bb [zsxwing] Remove `import StreamingContext._`
c15162c [zsxwing] Reorganize StreamingContext implicit to improve API convenience

12 files changed, 0 insertions, 12 deletions

diff --git a/examples/scala-2.10/src/main/scala/org/apache/spark/examples/streaming/KafkaWordCount.scala b/examples/scala-2.10/src/main/scala/org/apache/spark/examples/streaming/KafkaWordCount.scala
index c9e1511278..2adc63f7ff 100644
--- a/examples/scala-2.10/src/main/scala/org/apache/spark/examples/streaming/KafkaWordCount.scala
+++ b/examples/scala-2.10/src/main/scala/org/apache/spark/examples/streaming/KafkaWordCount.scala
@@ -22,7 +22,6 @@ import java.util.Properties
 import kafka.producer._
 
 import org.apache.spark.streaming._
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.streaming.kafka._
 import org.apache.spark.SparkConf
 
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/CustomReceiver.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/CustomReceiver.scala
index 6bb659fbd8..30269a7cca 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/CustomReceiver.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/CustomReceiver.scala
@@ -23,7 +23,6 @@ import java.net.Socket
 import org.apache.spark.{SparkConf, Logging}
 import org.apache.spark.storage.StorageLevel
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.streaming.receiver.Receiver
 
 /**
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/HdfsWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/HdfsWordCount.scala
index 6c24bc3ad0..4b4667fec4 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/HdfsWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/HdfsWordCount.scala
@@ -19,7 +19,6 @@ package org.apache.spark.examples.streaming
 
 import org.apache.spark.SparkConf
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 
 /**
  * Counts words in new text files created in the given directory
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/MQTTWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/MQTTWordCount.scala
index e4283e04a1..6ff0c47793 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/MQTTWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/MQTTWordCount.scala
@@ -22,7 +22,6 @@ import org.eclipse.paho.client.mqttv3.persist.MqttDefaultFilePersistence
 
 import org.apache.spark.storage.StorageLevel
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.streaming.mqtt._
 import org.apache.spark.SparkConf
 
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/NetworkWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/NetworkWordCount.scala
index ae0a08c6cd..2cd8073dad 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/NetworkWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/NetworkWordCount.scala
@@ -19,7 +19,6 @@ package org.apache.spark.examples.streaming
 
 import org.apache.spark.SparkConf
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.storage.StorageLevel
 
 /**
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/QueueStream.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/QueueStream.scala
index 4caa906591..13ba9a43ec 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/QueueStream.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/QueueStream.scala
@@ -22,7 +22,6 @@ import scala.collection.mutable.SynchronizedQueue
 import org.apache.spark.SparkConf
 import org.apache.spark.rdd.RDD
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 
 object QueueStream {
 
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala
index 19427e629f..c3a05c89d8 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/RecoverableNetworkWordCount.scala
@@ -25,7 +25,6 @@ import com.google.common.io.Files
 import org.apache.spark.SparkConf
 import org.apache.spark.rdd.RDD
 import org.apache.spark.streaming.{Time, Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.util.IntParam
 
 /**
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/StatefulNetworkWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/StatefulNetworkWordCount.scala
index ed186ea565..345d0bc441 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/StatefulNetworkWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/StatefulNetworkWordCount.scala
@@ -20,7 +20,6 @@ package org.apache.spark.examples.streaming
 import org.apache.spark.SparkConf
 import org.apache.spark.HashPartitioner
 import org.apache.spark.streaming._
-import org.apache.spark.streaming.StreamingContext._
 
 /**
  * Counts words cumulatively in UTF8 encoded, '\n' delimited text received from the network every
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterAlgebirdCMS.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterAlgebirdCMS.scala
index 683752ac96..62f49530ed 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterAlgebirdCMS.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterAlgebirdCMS.scala
@@ -23,7 +23,6 @@ import org.apache.spark.SparkConf
 import org.apache.spark.SparkContext._
 import org.apache.spark.storage.StorageLevel
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.streaming.twitter._
 
 // scalastyle:off
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterPopularTags.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterPopularTags.scala
index f55d23ab39..f253d75b27 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterPopularTags.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/TwitterPopularTags.scala
@@ -18,7 +18,6 @@
 package org.apache.spark.examples.streaming
 
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import StreamingContext._
 import org.apache.spark.SparkContext._
 import org.apache.spark.streaming.twitter._
 import org.apache.spark.SparkConf
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala
index 79905af381..6510c70bd1 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/ZeroMQWordCount.scala
@@ -24,7 +24,6 @@ import akka.zeromq.Subscribe
 import akka.util.ByteString
 
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.streaming.zeromq._
 
 import scala.language.implicitConversions
diff --git a/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewStream.scala b/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewStream.scala
index 55226c0a6d..fbacaee986 100644
--- a/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewStream.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/streaming/clickstream/PageViewStream.scala
@@ -19,7 +19,6 @@ package org.apache.spark.examples.streaming.clickstream
 
 import org.apache.spark.SparkContext._
 import org.apache.spark.streaming.{Seconds, StreamingContext}
-import org.apache.spark.streaming.StreamingContext._
 import org.apache.spark.examples.streaming.StreamingExamples
 // scalastyle:off
 /** Analyses a streaming dataset of web page views. This class demonstrates several types of