Added three new messages:
PriochangedMessage 	(server-->client): indicates that prio of players changed
BoardMessage 		(server-->client): sends the current situation on the board
UnregisterMessage:	(client-->server): cleint wants to leave thje game
Handlers (stubs) have been added as well.
Board class is very rudimentary so far...
Forgot to add some classes
Merge branch 'master' of https://github.com/florianeckerstorfer/foop-exercises