Demo Quality of Life, Item Rolling, and Bug Fixes

Added a new interface for selecting Nightmare level. This interface clarifies more specifically what changes when you change level as well
Each Nightmare Level costs 1 Boss Key from the previous level to unlock. Boss keys now always drop on the 5th consecutive boss kill in a run
50% of your Spirit is now lost when taking damage on Adventurer
Revamped item quality to scale in more interesting ways and generate better items
Reduced the amount of unusable trash dropping in Nightmare in general
Fixed a major level generation issue that could soft-lock runs
Fixed one memory leak
Fixed an issue that might cause gaps to appear in the end-of-run inventory screen
Added a delay for selecting upgrades to prevent them from being selected offscreen
Improved the performance when opening the Boss Chest
Fixed a bug where the Treasure Chest research node was causing odd behavior, including failure to save your research tree state
Fixed a variety of skill description issues (Thanks Moasseman!)
Fixed a mysterious skill tree line that was pointing to demo-locked skills
Improved the level geometry in the Warden's arena