Add premessage-deflate extension handler for HTTP WebSocket

Add premessage-deflate extension handler for HTTP WebSocket.

Motivation:
- Need to compress HTTP WebSocket frames payload.

Modifications:
- Remove UTF8 checking of WebSocketFrames from frame decoder in order to
allow compressed frames to go to the next handler.
- Add a WebsocketPremessageDeflateHandler to initialize the frame deflater/inflater if client is compatible with deflate extension.

Result:
First version of the implementation for feedback.
It's because the permessage-compression draft (at http://tools.ietf.org/html/draft-ietf-hybi-permessage-compression-18) allows to receive TEXT frames with a compressed payload.

I chose to remove UTF8 checking in order to handle the frame compression in an external handler and not within the websocket frame decoder. Otherwise we can choose to create a new API for extensions (eg. WebSocketExtensionHandler) and pass them as parameter of the WebSocketServerProtocolHandler constructor.