Added new feature: Named stream output and ability for the downstream pellets to subscribe for one or more named streams.
Updated:
1. Thrift definition to associate a list of subscribed named streams to each edge. (empty=default).
2. Updated app builder api to allow subscribe with or without specifying stream name (if no stream name is specified, it is subscribed to the DEFAULT_STREAM. NOTE: DEFAULT_STREAM is not same as all streams).
3. Updated emitter to support emitting to default stream as well as any named stream.
4. updated flake sender to filter messages to be sent to particular edges using the subscribed stream names (Used ZMQ PUB/SUB mechanism.. pretty awesome.. LOVE ZMQ!!)
5. minor udpates to the resource mapping class required to forward the stream names and subscriptions to the containers.
6. added new samples: A MultiStreamWordPellet which generates two named streams. And a sample application using this pellet which create two consumers each subscribing on one or more named streams.

Fixes #15