Animation now with no trailing colors

Set another setTimeout within initial setTimeout for general animations
to turn the purple into white, again. This will make the zombie look
more like it's traversing through the grid.

I MIGHT (and probably should) create a tweening-like animation between
cells to give a more smooth animation. This could be a parabolic
animation speed (gradual slow, fast, slow). Of course, this will be
after I implement some form of A* path algorithm and my own "zombie's
aren't supposed to be that smart at finding things" algorithm.