Load Images for Snake instead of rectangles

Instead of rectangles, loads a tail image, body image, and head image (I made some awesome 16 x 16 pixel pings in inkscape). 

The tail takes a couple of steps to "load" (I think the effect looks kind of cool, sort of like the snake is unwinding at the start). 

Potential issues:
1. The delay in refreshing causes the tail to appear in two places at once briefly.
2. Need to decide if the head should be oriented.

Since we're just worried about basic functionality right now of loading images, I believe this does the job and we can address the above issues next. 2) depends on the actual image we will use for the head, and 1) is a separate topic.

closes #4