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.