More fixes & Game Over

- Fixed a bug where a centipede that is in the process of dying is still
moving and could kill you
-Added invulnerability after the player 'respawns' because it was really
easy to immediately run into a centipede attack the planet.
-Running out of atmosphere causes a game over
-Made a game over function in the Game Controller
- Game Over now spawns text telling you it's a game over, how you
failed, and how to restart the game
- My friend made a short game over music loop based off the background
music theme that plays when you get a game over