[WIP] Enemy HP bar

[jroweboy]

Based off the UI changes I've made, this change adds an Enemy HP Bar for the last attacked enemy.

The code is currently a spaghetti mess. Turns out its really complicated to add this, so it may not be worth reviewing until I get a change to clean it up. I'm opening a Draft Pull Request now since its getting close to being ready, and if you wanted a general idea of what the code will be like and have some time to look it over, I feel I might as well open the PR early then.

TODO List: Features:

• [x] Base enemy HP bar for last attacked enemy.
• [ ] Auto hide on area change.
• [ ] Auto hide on enemy despawn
• [ ] Hide HP bar after enemy dies
• [ ] Hide HP bar after a certain time limit. (Maybe don't need?)

Bug fixes:

• [ ] Certain combinations of HP/Max HP are displayed incorrectly so the enemy HP sometimes partially "refills".
• [ ] HP above 255 may not work properly (needs more testing)
• [ ] Probably more when mattrick gets his hands on it.