[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.
[FLINK-1031] Fix POM files to support Eclipse
Update LICENSE and NOTICE files

[ci skip]
Consolidate some third-party license entries, update readme in binary distribution

[ci skip]
Add Netty to License files

[ci skip]
[FLINK-989] Improve error message when not finding enough task slots.
[FLINK-1030] Refactor and clean up instance managers.
Reworked, improved, and testes split assigners
Redesign Scheduler from pre-assignment to more flexible schedule-on-demand model
Adapt RPC to support primitive types as parameters and return values.
Redesign Scheduler part 2