Added TileFactory.java and GrassTileFactory.java
GrassTileFactory.java now correctly implements createTile()
Added PathTileFactory.java used to create Path Tiles
Removed unnecessary methods from GrassTile.java and PathTile.java
Added a tileIdMap to the MapLoader.java class. This map maps tile ids to tile factories.
Removed some parameters from the createTile() method in the TileFactory subclasses. Moved Pixmaps of tiles to their appropriate tile factories. Also moved the tile size to the TileFactory class
Changed Tile.TILE_SIZE in GameMap.java to TileFactory.TILE_SIZE, since I moved the constant to the other file
Merge branch 'towerdefense' of https://github.com/duke-compsci308-spring2013/vooga into towerdefense