Changed path to imagePath for clarity.
Can now check for vertical exits. (More...)
Fixed a bug whereby entering the grid threw an exception due to a null being returned for the room position at (), -1) or (-1, 0).
Removed unused imports.
Fixed a bug where the vertical and horizontal exit images were not overlapping the MapSquare borders.  Created methods to remove the default border and replace it with a matte border that only exits on appropriate sides, and also to restore the default border again on mouseExited() should no exit be drawn.  Also re-added the Room.png image, rather than relying on the border method.