Graphics Update and enemy and tower preferences are loaded from a file

Updated the tile sprites.  Enemy and tower preferences are loaded from
an external file now.
Tower Upgrade, Tower Sprites and Win/Lose Menu

Added all Tower sprites and added upgrading.  All tower sprites have
animations for attacking.  Added a Win/Lose Menu that shows at the end
of the map.  It allows the player to go back to the level select screen
and try another map
Code Merge

Merged Levy's branch to this.  Minor updates and bug fixes with towers
and ui