Crash fixes and GameOver/Success changes

-Fixed the RobotScript crashing the game on unloading a scene by trying
to access the GameController
- Fixed the game crashing when the robot crashed while holding a mineral
-Succesd/gameover scripts back to menu buttons now navigate back to menu
- the Z positions on the grid are now set to makes sense depending on if
they're in the foreground, background, or center. All positions should
now be whole numbers or .5 exactly to make it easier to deal with.
-Arrow commands are always on top of everything except for the robot