Change EggCrate -> EggCarton
Clean up EggCrate -> EggCarton change.
Use EggConveyor instead of Ground place-holder.
Remove old ground.js
Add root transform to CANVAS

Add a root transform to the CANVAS context so that all the drawing code
works in the Box2D coordinate system. The transform puts the origin in
the lower-left corner, with y-positive going up. Note that this means
all the images will be upside-down.