[FLINK-2451] [gelly] removed redundant examples; added comments describing which gelly method each example illustrates.

 - enabled .declareStream() and connect via stream name
 - enabled multiplt output streams
 - added .split() / .select() / strip pattern
 - added helpers in new package utils
 - adapted and extended JUnit tests
 - adapted examples
some minor improvements (FlinkClient, integration of Tuple0)

This closes #1011

[FLINK-1901] [core] enable sample with fixed size on the whole dataset.

[FLINK-1901] [core] add more comments for RandomSamplerTest.

[FLINK-1901] [core] refactor PoissonSampler output Iterator.

[FLINK-1901] [core] move sample/sampleWithSize operator to DataSetUtils.

Adds notes for commons-math3 to LICENSE and NOTICE file

This closes #949.

The DataExchangeMode of union nodes was not respected when translating an OptimizedPlan
to a JobGraph. This could result in deadlocks, when a branched data flow was closed.

Union nodes with a batch exchange will propagate their exchange mode to all inputs of
their inputs when the JobGraph is generated.

This closes #1036

This decouples the building of the StreamGraph from the API methods.
Before the methods would build the StreamGraph as they go. Now the API
methods build a hierachy of StreamTransformation nodes. From these a
StreamGraph is generated upon execution.

This also introduces some API breaking changes:

 - The result of methods that create sinks is now DataStreamSink instead
   of DataStream
 - Iterations cannot have feedback edges with differing parallelism
 - "Preserve partitioning" is not the default for feedback edges. The
   previous option for this is removed.
 - You can close an iteration several times, no need for a union.
 - Strict checking of whether partitioning and parallelism work
   together. I.e. if upstream and downstream parallelism don't match it
   is not legal to have Forward partitioning anymore. This was not very
   transparent: When you went from low parallelism to high dop some
   downstream  operators would never get any input. When you went from high
   parallelism to low dop you would get skew in the downstream operators
   because all elements that would be forwarded to an operator that is not
   "there" go to another operator. This requires insertion of global()
   or rebalance() in some places. For example with most sources which
   have parallelism one.

This also makes StreamExecutionEnvironment.execute() behave consistently
across different execution environments (local, remote ...): The list of
operators to be executed are cleared after execute is called.

[tests] Replaces Scala mixins for the Job/TaskManager with classes which extend the respective classes. Adds proper logger registration for sub-classes of FlinkUntypedActor.

This closes #1022

This closes #1004

This closes #977

[tests] Hardens TaskManagerRegistrationTest.testTaskManagerResumesConnectAfterJobManagerFailure test case by checking testing actor's complete mailbox for a Terminated message

Closes #1025

Closes #1014

Closes #994

[FLINK-2521] [tests] Adds TestLogger class which automatically logs the currently executed test names and the reasons for a failure.

Makes test bases extend TestLogger to add automatic test name logging

Frames test logging statements to make them more prominent

This closes #1015.

[tests] Reinforce StateCheckpoinedITCase to make sure actual checkpointing has happened before a failure.

[FLINK-2462] [streaming] Major cleanup of operator structure for exception handling and code simplication

  - The exceptions are no longer logged by the operators themselves.
    Operators perform only cleanup in reaction to exceptions.
    Exceptions are reported only the the root Task object, which knows whether this is the first
    failure-causing exception (root cause), or is a subsequent exception, or whether the task was
    actually canceled already. In the later case, exceptions are ignored, because many
    cancellations lead to meaningless exceptions.

  - more exception in signatures, less wrapping where not needed

  - Core resource acquisition/release logic is in one streaming task, reducing code duplication

  - Guaranteed cleanup of output buffer and input buffer resources (formerly missed when other exceptions where encountered)

  - Fix mixup in instantiation of source contexts in the stream source task

  - Auto watermark generators correctly shut down their interval scheduler

  - Improve use of generics, got rid of many raw types

This closes #1017

This closes #1029

This closes #1018

[FLINK-2527] [gelly] Ensure that VertexUpdateFunction.setNewVertexValue is called at most once per updateVertex

This closes #1027

[FLINK-2458] [FLINK-2449] [runtime] Access distributed cache entries from Iteration contexts & use of distributed cache from Collection Environments

This closes #970

This closes #1021

This closes #1009

PlanBinder methods were restructured to make the class more readable.

Keys are now stored as strings to simplify string-key-expression support.
Parameter retrieval was moved from PB to OI constructor, similiar to PythonOperationInfo.
This change reduces the clutter in Planbinder and allows code reusage for operations with similar parameters.

This closes #961

 - extended TupleType helper classes to handle Tuple0
 - extended TupleSerializer to handle Tuple0
 - included Tuple0 into JUnit tests
 - simplified Receiver.createTuple(int)

This closes #983

This closes #1013

Correcting commit, because the wrong commit was pushed earlier.

1. Allow access to Runtime Context from I/O formats.
2. Make all existing I/O formats context aware.

This closes #966.

[CLEANUP] Add space between quotes and plus sign in String concat for readability in flink-yarn module

While working on Flink on YARN, do some simple nit cleanups to add space between quote and plus sign for readability in yarn module for readability.

Use StringBuilder instad of StringBuffer in FlinkYarnClient since the String materializes immediately, so no need synchronize protection.

Author: hsaputra <hsaputra@apache.org>

Closes #1010 from hsaputra/cleanup_yarn_branch and squashes the following commits:

a6fc9e1 [hsaputra] Add space between quote and plus sign for readability in flink-yarn module.