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)
I cannot make it the same name as the binary, because the "main" package and the "collider" package cannot live in one folder. So I have to put "main" in a folder different from "collider".
What about renaming wsmain to collidermain, wsserver to collider?