Walk Animation Redux

Walk animations have been updated with the new sprite sheet and encompass
all movement directions including with cores. Sprite still faces up when stopped.
Removed old assets, fixed core pickup bug
OMG YES MOVEMENT

Movement is totally awesome now. Sprite stops in the same direction is was moving.
Sprite doesn't keep animating when you run into a wall.
Hell, you can't even _turn_ into walls anymore, it's just that good.
I sped up movement and animation speed. Overall, I like the feel of this much better.
Merge branch 'TheEmperorsNewGroove'