Capturing of buildings

- You can now capture an building. No visuals changes yet. Just in the
background.
- Capture points remaing when moving off the building. It will slowly
decrease each turn.
- When an enemy is going unto the building that the other player was
previously capturing you will use the current capture points. This
increases tactics and speeds up the game.
- If an enemy is trying to capture your building and you move a friendly
unit unto the building (after destroying the enemy unit which was trying
to capture the unit) you reset the capture points.