added image loader class. Loads up images and allows retrieval of loaded
image.

added a zombie.png sprite map and a zombie.json file which maps portions
of the png to different poses.

added a TODO file which outlines some tasks to be done.
got the code to a point where there is a zombie doing his walk animation
on the front. however, the game is not working yet.  I need to integrate
the animations with the graphics renderer etc.
When zombies load they load as walking!