Add callback to obtain handshake response as client in case of handshake failure.

This provides a listener callback to obtain the server's handshake response in case it was rejected with a HTTP status code != 101.

E.g. if the server rejects the WebSocket upgrade request by issuing a
HTTP response with 503 status code, then this HTTP response data can be
obtained via
WebSocketListener.onWebsocketHandshakeReceivedAsClientFailed(WebSocket,
ClientHandshake, ServerHandshake).

If there already is any other way of obtaining the server's response including http status code, please enlighten me :) Thanks / Christoffer