Streaming addon prototype

Support for low latency streaming jobs.

The API provided is fairly similar to the batch one, for example see our [WordCount](https://github.com/mbalassi/incubator-flink/blob/streaming-ready/flink-addons/flink-streaming/flink-streaming-examples/src/main/java/org/apache/flink/streaming/examples/wordcount/WordCountLocal.java).

Legal issues were extensively discussed on the mailing list. 

Further work is needed for fault-tolerance, state management and cluster performance optimization.
The connectors package is under heavy development right now, the refactored code is going to be pushed to the pull request during the end of the week.