[FLINK-1004] Add the maven repositories for all vendors + documentation

This closes #62
Improve error messages for data sinks inside iterations.
[FLINK-1018] Add tests to verify correct placement of pipeline breakers with broadcast variables
[FLINK-1018] Fix cross pipelining/daming info to resolve cross-related streaming deadlocks.
[FLINK-828] Implement accumulator example

- shows how to build a custom accumulator (for vectors)
- employ that accumulator for obtaining filter statistics

This closes #55.
Reconfigure Apache Rat to enforce the correct ASF license header
Fix Quickstart example (by using the latest 0.5.2 Stratosphere release)
Fix scope for scalatest dependency
Improve exception messages for file output format when target file cannot be created.
[FLINK-955] ResizingHashTable: automatic resizing, IndexOutOfBoundsException fixed, pointers

This closes #57
[FLINK-1026] Fix PojoComparator

Was not using the user code class loader and therefore could not clone
the serializer that is internally used.

Also modify KMeansForTest to make use of the PojoComparator to prevent
such bugs in the future.

Also fix PackagedProgramEndToEndITCase, AvroExternalJarProgramITCase and
the external jar file class loader tests in flink-clients. The pom was
not configured to remove the code that should only be in the external
jar from the test-classes directory.