Fixed missiles objects, rock objects, missile sound etc.
Helper functions moved from Game to Helpers
Helper functions moved from Game to Helpers (commited missed change)
Added semicolon.
Added the great nebula image
Added actual_size and radius for sprite
Added score, lives and gameover text drawing
Fixed ship-rock collision
Removed old obsolete code from Explosion's draw method
Changed font for 'gameover'
Explosion class removed, small refactoring