disableProtocolCheck option and close() method

Because the Tessel implementation of WAMP in `wamp-tessel` does not (cannot, apparently) pass the protocol of "wamp.2.json" during websocket connection, I added a flag to the options disable the protocol check. This is similar to what has been done in crossbar.io itself (see http://crossbar.io/docs/WebSocket-Options/) 

I've also added a close() method that can close the underlying websocket server. This is necessary if you need to spin up one instance after another on the same port, for example while going through test cases.