XP gain popups
Giving CanvasScaler a try.
- implemented a basic progress bar using the new GUI components
- XP positioned where mobs died
- added level script event for choosing the random spawns
Full implementation of new 4.6 UI progress bar and editor.
Hooked up the XP bar in the portrait, revamped the leveling logic and math.
Fix NRE when possessing a tank.
Multiple tiers will now skip during if gained previously.

Small tweak to GREENK0 behavior.
Added a fraction to show the overwhelmed herolings needed in the overwhelm progress bar.