More refinements

-Buildings can no longer be built on unbuildable terrain (GTDMap /
GTDGame).
-Buildings can no longer be built on other buildings (GTDMap / GTDGame).
-Player money implementation now in place (GTDPlayer / GTDGame)
-Buildings now take away from a players money (GTDGame / GTDPlayer)
-Cleaned up some code into separate functions (GTDGame)
-Unit x/y values are now the center of the building (previously the top
left corner; GTDGame). Drawing of units changed to reflect this change
(GTDMap)
- Specific building collision values / costs can now be retrieved
statically (useful when the specific units aren't instantiated). Static
functions for the remaining elements (and for units) will be added.
(GTDUnit)
-Fixed rectContainsUnit (GTDMap).
Map altered to look better.