Added music, SFX and a better menu!

Due to the hurry in the  godot-wild-jam-70 my game didn't feature any music and sound. To finish my game with a more "complete" feeling I have added the following things:

• some music and SFX's
• a better menu for restarting, speedruning and time and audio sliders
• polish for the last few sections

hopefully this makes the game a bit more enjoyable!