Tile.java now extends Sprite.java. Tiles now paint themselves on the map. Removed the unnecessary paint gridlines method in the MapScreen.java class
Change the order of painting in MapScreen.java so that game elements are painted after tiles are painted. This ensures that GameElements are not overlapped by tiles
Merge branch 'towerdefense' of https://github.com/duke-compsci308-spring2013/vooga into towerdefense