Fixed the ActionPoint property of the Entity class.

The BoundingBox is now stored relative to the upper left corner rather
than the ActionPoint. This greatly simlifies the math of changing the
action point which is now only maintained by the relative location of the
drawing box.
Made map textures seamless.

A feature in Gimp that helps remove the notable transitions between each
tile. It wasn't entirely successful and it does distort the texture a bit,
but I think the overall effect is better.