Add test to verify that a player can only create one headquarter
Add test to verify that two players that have placed headquarters can also place additional buildings
Added tests for checking if a player can attack a certain building. Updated the model to handle this.
Updated TODO list
Added tests for placing flags and roads when several players and made the methods that don't require the player to be set only work when the default player is used. Also discovered and fixed a problem with how the scout works with these changes and added an extra test.