Tested and fixed Object-Wall collision

- Added a TODO to figure out stuff
- Objects now have a direction vector based on the last direction they
walked into.
- Removed unneeded headers from CollisionHandler.
- Added an isWalkable function to the map and the AIMesh
- AIMesh has a TranslateToTextureCoordinate. Don't use this, for real,
this is for my debug purposes. The translation is done by the system for
you.