Fog of war

- The fow is now implemented. 3 days (turns) it is days and 2 days
night.
- Nothing has been added to the movement of units. So moving a unit
during the night will not update the fow. Only when the NextPlayer()
method is called.
- There are 2 methods each with 2 overloads which allow you to show or
hide the fow for a unitgameobject or an buildingameobject. This can be
used for the movement.
- Every building and unit has a method from which to retrieve the line
of sight. This is used to hide the fow.