SockJS Protocol support for Netty.

Motivation:
Provide support for SockJS [1] which is a WebSocket emulation protocol
which can fallback to different protocol in case WebSocket support in
not supported.

Modifications:
Added a codes-sockjs module which contains all the code.

Result:
SockJS clients can now be used with a Netty server configured with
SockJS.

[1] https://github.com/sockjs

This [gist](https://gist.github.com/danbev/691bca06d5e0e7ff65ab) is a suggestion intended for Netty's [documentation](http://netty.io/wiki/index.html). 
Check if heartbeatFuture != null ?