Accept all WebSocket subprotocols.

Now that Play uses Netty 3.7.0+ we can use the wildcard WebSocket subprotocol. This allows Play to accept arbitrary WebSocket subprotocols like 'wamp' used by the WAMP WebSocket RPC/Pubsub JavaScript library. Before Netty would just throw an exception.

This PR will also finally close #1101 and #800.

I've compiled this PR and it works as expected with the WAMPlay library.

Thanks!