[FLINK-1017] Add documentation for execution parallelism

This closes #114
Updated documentation figure: FlinkOnYarn.svg

This closes #110
[FLINK-629] getFieldNotNull added to Tuple and updated Aggregators and Comparators to use that where appropriate
[FLINK-629] Updated getFieldNotNull usage and added it to TupleSerializers

This closes #73
[FLINK-1063] Revert race introducing commit

This reverts "[FLINK-998] Close network connections when idle" [1] as
it introduced a race condition into the network stack, which might
result in a re-ordering of network envelopes.

[1] 52512636444902497e47ccbfb1cabaffb3e23343
[streaming] Fixed SlidingWindowStateIterator
[streaming] Reduce operator added to ConnectedDataStream + test
[streaming] Updated directed emit to not use output names when all outputs are selected
[FLINK-1080] [streaming] Streaming aggregation added

Conflicts:
	flink-addons/flink-streaming/flink-streaming-core/src/main/java/org/apache/flink/streaming/api/datastream/DataStream.java
[streaming] Added TypeInfo to DataStream
[FLINK-1080] [streaming] Streaming aggregation update and refactor
[FLINK-1058] [streaming] Streaming initial documentation
[streaming] DataStream type refactor for easier future extensions
[streaming] Invokables and tests added for fast batch/window reduce operations and aggregations
[streaming] window and batch operator added to DataStream + Documentation updated accordingly