Capture buildings and small code refactoring

- Added the first version of capturing and calculating the capturing of
buildings. No visuals yet.
- Changed the Dictionary of players to a SortedList. This way we can
easily switch between players without the use of alot of if statements.
See the NextPlayer() method for more detail.
- Added an PlayerIndex index property to the player class and removed
the currentPlayerEnum since it can be retrieved via the currentPlayer
object.