[scala] Self-contained build for scala examples

This closes #199.
[FLINK-1218] Replace new Integer with Integer.valueOf in tests

This closes #183.
[FLINK-1239] [streaming] IterateExample fix and parallelism setting in StreamExecutionEnvironment made public

Conflicts:
	flink-addons/flink-streaming/flink-streaming-examples/src/main/java/org/apache/flink/streaming/examples/iteration/IterateExample.java
[FLINK-1233] Fix flaky AggregateITCase
[FLINK-1237] Add support for custom partitioners
  - Functions: GroupReduce, Reduce, Aggregate on UnsortedGrouping, SortedGrouping (Java API & Scala API)
  - Manual partition on DataSet (Java API & Scala API)
  - Distinct operations provide semantic properties for preservation of distinctified fields
  - Tests for pushown (or not pushdown) of custom partitionings and forced rebalancing
  - Tests for GlobalProperties matching of partitionings
  - Caching of generated requested data properties for unary operators