added methods to Sprite class
merged pull conflicts
Merge branch 'towerdefense' of https://github.com/duke-compsci308-spring2013/vooga into towerdefense
added MapSelectorScreen and LevelSelectorScreen and their images
Merge branch 'towerdefense' of https://github.com/duke-compsci308-spring2013/vooga into towerdefense
Merge branch 'towerdefense' of https://github.com/duke-compsci308-spring2013/vooga into towerdefense