Changed: ClientHandler to only throw User.UniqueID as exception data if User is not null
Added: DisconnectClient on ClientHandler, if the client does not supply correct username and password he is told he has been kicked off and the stream is closed and TcpClient disposed.
Changed DummyDatabaseHandler to catch all exceptions
Changed ServerHandler to only fire OnClientDisconnect event if the exception data field has been filled with user uniqueID, since the client wont be added to the list of all connected clients if he does not supply valid login information, then there is no need to fire the event and try to remove the non existent client.