The Themes Update!

This update adds themes, which revamp the user experience depending on
which theme is randomly chosen. Themes include a special background for
MainGUI and TeamGUI, special color schemes, and a special soundtrack
matching the UI.

Main Changes:
- Theme enum within MainGUI dictates changes
- changed some labels/buttons to be more readable and to match themes
- added button color customization
- added custom health bar with percentage display
- reformatted some code for readability
- changed some button type colors
- refined button borders for clarity
- unified fonts for broader compatibility (Windows intended)
- new files: music and backgrounds in respective locations

Themes added in this update: GROUND, WATER, ROCK

warning: **large download!**