Ambush 1.1 - Bug fix

I found a bug in ambush, quite a game-breaking one(Basically, when you upgrade your ship, the health upgrade would be free for the rest of the upgrades). I managed to fix it - I found that there was a line of code where it shouldn't be, so that was deleted and the bug was resolved. I've also added icons for the game over menu.

The game is pretty much done now. I haven't found anything else that needs fixing.