0.8 Music Easter Egg, 11 new treasures, new treasure system, difficulty updates.

- Added music easter egg. - Added 11 new treasures. - Removed Christmas hats. - Reworked treasure: treasure is now free, and accessible every 3 rounds from any of the multiple chests present throughout the map. - Fixed issue where round would tick over early. - Witch zombies are now only present on round 10 and up. - Adjusted special enemy spawns for early rounds. - Adjusted early zombie health. - Adjusted early zombie speed. - Lowered slicer damage. - Fixed visual bug in doorway to sacrifice room.