[FLINK-970] Adds first() operation on DataSet, UnsortedGrouping, and SortedGrouping

This closes #88
Added parameter checks and tests for first-n operator.
Excluded DataSet.first(), UnsortedGrouping.first(), and SortedGrouping.first() methods from ScalaAPICompletenessTest.
Added documentation for first-n operator.
[FLINK-1104] [streaming] Eliminated Tuple1 from connectors
[streaming] Streaming jobgraph and vertex refactor to match recent runtime changes
[streaming] added batchReduceGroup, windowReduceGroup functionality to ConnectedDataStream and GroupedConnectedDataStream
[FLINK-1102] [streaming] Projection operator added to DataStream

Conflicts:
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java

Conflicts:
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/JobGraphBuilder.java
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/StreamConfig.java
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/ConnectedDataStream.java
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java
[streaming] Fixed InternalStateTest to avoid printouts + minor StreamVertexTest fix
[doc] [streaming] Added Twitter connector & Projection operator to docs
[FLINK-1103] [streaming] Updated WordCount example to become self-contained and removed old TestDataUtil
[FLINK-1121] [streaming] minBy and maxBy operators added to streaming api