Game language update!

Two new features have been added, and some have been tweaked

- Feature 1: A button in the main menu to toggle sounds and music

- Feature 2: A selector to select between 3 different languages, EN, NL and AA

The spawning and moving systems now use deltatime to be more consistent over devices with different FPS

New background image for the graveyard

Red zombies are now 4x as slow as the blue zombies, which balances with their health