Added image scene to render an image in a scene. There is also now
a testing image that is an uber meme. Currently the problem is
that the spritebatch cannot use the offsetof macro because it is a
templated class. Possible solutions to this are changing it to be
specifyable or implemented per vertex type as the other batches
have been.
The sprite inherits from Poseable. It is intended to allow for
pure 2D rendering or integration of sprites/particles into 3D
scenes. Eventually an ImageScene should be created to test out the
image loading, sprite movement and rotation, and 2D camera
functionality for the builtin engine.