websocket streaming sample, and gwt-20 client sample.

I would like to submit for your consideration two new atmosphere samples:

- samples/websocket-stream: a simple client/server application showing how to stream data in a long-lived manner from a server to a client
- extensions-samples/gwt/gwt20-websockets: a simple client that can attach to the websocket-stream server, showing how to incorporate websockets into gwt. This is based on the com.sksamuel.gwt package (https://github.com/sksamuel/gwt-websockets). I am building these as a proof-of-concept, and I hope they will prove useful to others.

Note: the minor change to the websocket-chat/web.xml file is to bring it into compliance with the servlet spec with respet to the async-supported tag order.

Thank you for creating such a wonderful OSS project.

Simon.