Removed TILE_SIZE field from the tile class because it was superfluous, since we already had TILE_DIMENSION as a field. Also put the Tile.java class within a tiles package in the model package. All future subclasses of Tile objects and potentially tower factories will be within this package
Merge branch 'towerdefense' of https://github.com/duke-compsci308-spring2013/vooga into towerdefense