No longer use socket as key in maps, instead, use the session id. Only use the session id in the sender thread, "resolve" it to the socket only in the moment when it is needed. Outstanding requests will be detected to have an invalid session id then.
Also, as side effect, fixed an issue with two callback classes which were named the same and caused unexpected behavior.
Sender thread output queue is now limited.
Server thread now terminates correctly.
Now cloning packets when sending them to multiple recipients.
Fixed one thread issue - GameStart still needs to be made thread safe.