Fixes a lot of minor UI issues, performance issues, and optimizes memory/loading. Also fixes a few bigger issues:
* Boss names could copy from one to the next if you left the boss editor window open when returning to the overworld editor.
* Physics objects were being removed from a room when the boss was destroyed and not respawning.
* Items were spawning at slightly incorrect sizes under certain conditions.
* Jumping enemies were hitting the ground and sliding infinitely under certain conditions.
* Graphics artifacts were getting stuck on screen transitions.