This closes #1467

- removed BoltWrapperTwoInputs
- add generic multi-input stream bolt wrapper
- updated FlinkTopology to translate multi-input bolts correctly
- added multi-input union test wrapper
- updated FlinkTopology to translate multi-input bolts correctly
- added multi-input union test

This closes #1456

[FLINK-3166] [runtime] The first program in ObjectReuseITCase has the wrong expected result, and it succeeds
- TestEnvironment now honors configuration of object reuse
- Fixed reduce transformations to allow the user to modify and return either input

This closes #1464

This closes #1472

WriteMode has 2 values NO_OVERWRITE and OVERWRITE but it refers CREATE in the javadoc.
Probably old code.

This closes #1475

[FLINK-3103] [runtime] Remove unnecessary synchronization in FsStateBackend.FsCheckpointStateOutputStream

This closes 1474

This closes #1473
This closes #1098
This closes #1459

- The off-heap stats reported by the memory logger didn't include direct memory.

This closes #1466

This closes #1444

This closes #1255

Enalbes submission of Flink programs written in Clojure.

This closes #1457

- use AMRMClientAsync instead of AMRMClient
- handle allocation and startup of containers in callbacks
- remove YarnHeartbeat message

The AMRMClientAsync uses one thread to communicate with the resource
manager and an additional thread to execute the callbacks.

This closes #1450.

This closes #1463.

This closes #1439

This closes #1442

- Memoize string representations of AbstractID.
- Use lookup table for byte-to-hex conversion in StringUtils.

This closes #1455

Before, when the Kafka Source would emit a final Long.MAX_VALUE
watermark to signal the end of elements (i.e. no partition assigned).
This would trip up the AutomaticWatermarkContext and the
NonWatermarkContext.

Now, a Long.MAX_VALUE watermark is allowed through.

[FLINK-3171] [misc] Consolidate zoo of wrapper classes for input/output-stream to data-input/output-view.

[hotfix] Minor cleanups in classes FileSystem, OperatingSystem, CopyableValue, GenericCsvInputFormat

This was removed in 3b8b4f0f. The
issue was fixed by this, but it disabled local testing as well.

This change re-introduces the variable and sets it to the empty
string by default. This way, we can still use the proxy server for
local testing.

This closes #1449

Many browsers don't allow cross-origin HTTP requests if the respective
HTTP header is not set by the server.

Because of this it was not possible to test changes to the web frontend
with the local proxy server and a running job manager.

See here: https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS

This closes #1418

This closes #1422

Kafka sources that don't read from any partition never emit a watermark,
thereby blocking the progress of event-time in downstream operations.
This changes the Kafka Source to emit a Long.MAX_VALUE watermark if it
knows that it will never receive data.

This also changes the Timestamp Extraction operator to reacto to a
Long.MAX_VALUE watermark by itself emitting a Long.MAX_VALUE watermark.

Before, would throw a ClassCastException when emitting watermarks with
timestamp/watermark multiplexing disabled.

This closes #1416

This closes #1441.