Character skins and power attacks!

- 2 character skins each Valkyrie
- Skins offer an additional powerful attack that can be manually used like a "special power"
- Moved Boss HP bars to prevent overlapping UI
- Fixed EXP Bug
- Increased amount of EXP needed to level up

Please note that the special attacks may be swapped out for different attacks at a future date, we are still working on improving the attack types.