Add a websocket signaling server impl

PTAL
(Sorry for the previous abandoned requests. I'm new to the github work flow and messed up the repository)
Oh, I get it. You don't want to send messages back to the sender.  I think it could be worded more clearly.  Perhaps something like "add message for all clients in the room except for the sending client".

Also, I think if one method is "add", this one should be "add" as well, but perhaps one should be "addToClient" and the other "addToRoom".