Made the main robot into a floater again.

With the reduced gravity and still no friction,
   the pyramid shape was annoying because it was
   so easy to zoom into the air and not come down
   for a while.
Made hacky conveyor belts:

They always point in the +x direction.
They can move a single rubble tile up an incline,
   but they can get clogged by more than one that are
   too close to each other.