Implement WebSocket Server

Implemented the Websocket Protocol on top of NanoHTTPD.
The NanoWSD Server will handle all incoming Websocket handshakes and return a special Response object, which blocks in its send(OutputStream out) while the Websocket connection is active. In order to overwrite the send method, it had to be made protected in NanoHTTPD.

The class NanoWSD could also extend SimpleWebServer, so that i could also serve files.