Added endgame conditions

This defines endgame conditions in the Game object, which means it is universal for all maps. We may eventually move this to the map, but it is less complicated to keep it in Game for now.

We also need to fix the endgame message, but I'm not sure with what. Right now its quite disappointing to win a game, I feel that losing might be more rewarding. Maybe this will come with the gui when we can show something to the player for winning.

Fixes #84.