New graphics for the terrain + Bunny colors

I simplified the terrain to just a few graphic shapes.

They're much simpler and I can place them higher or lower to raise/lower the ground. 

The ground pieces are made of circles on top of rectangles, so it ought to be easy for making the collision shapes for them - just use a circle shape and a rectangle shape and Godot seems to do well with combining the two.

I also colored the bunny graphics to make the different bunny colors that will be in the game.