Fuel Bar + Snapping changes

- Added a fuel bar with editable decay rate. The art is temporary so
feel free to change it.
- Robot now snaps to the arrow much more smoothly
- Arrows now snap to the nearest square properly
- Can no longer move robot in the planning stage with arrows
- Added a gameover function to Gamecontroller. Currently it does
nothing, but it should ideally do all the game over work so that it can
be easily called from other objects that can cause a game over.