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)
of maybe:

if clientMsgs, found := cache.data[roomID][clientID]; !found {
  cache.data[roomID][clientID] = clientMsgs{roomID, clientID}
}
clientMsgs.msgs = append(clientMsgs.msgs, msg)