Improve game model.

Add game_type to game to identify game mode: 'SINGLE' or 'TEAM'.
Add possibility to forced game finish.
Add new game_status 'ABORTED' to identify games that was forced finished without having 10 goals.
Add game state validation before game start - check for game mode and players count - team game should have two players in each team and single game mode should have one player in each team.