Reorganized the methods in Piece. Forgot to switch to branch...
Implemented Player money
ProductionBuilding.produceUnit now checks if the owner of the Building
has enough money before producing the Unit
Implemented get_damage in DamageMatrix.java
Added some sample test cases to make sure I'm not dumb
Updated the call structure since we Unit doesn't need to call Board for
damage.
Merge branch 'flexible_menu'
Added proper symbols to Map
Put in a generic Menu type. Trying to figure out how to proceed.
Merge branch 'master' into flexible_menu

Conflicts:
	src/building/Airport.java
	src/building/Base.java
	src/building/Building.java
	src/building/Port.java
	src/unit/Unit.java
Added some more structure around Pieces
Finished implementing the flexible menu system.
Current limitiations: you cannot go to the previous menu when you select
a Piece's action.
Clarification: there's three constructors for Menu. This determines (in
order):
	1. Top menu (children are all the Pieces)
	2. Piece menu (children are all the Piece's possible actions)
	3. Action menu (children is null)