Sounds! (and other stuff)

I had many requests to add sounds to the game, it is now done! I have added sounds for the main game events. Some might be reworked in the future, so please share if any of them is really annoying.

Other additions:

• Perk to increase the frequency of meteor showers
• Tweaks for score visualisation
• Fixing a bug that didn't properly remove the close call related perks
• Some refacto to prepare for future updates