Reinstated 4.x hacks, but using null checks and Harmony traverse API where possible

Major rework of how the background color is pushed to the game, and general code cleanup

Version 4.3:
- remove obsolete save compatibility hack in hopes of fixing compatibility with other folks' mods

Version 4.2:
- 2.0.202.48 beta compatibility fixes
- code cleanup

Version 4.1:
- code cleanup (no functional changes)

Version 4.0:
- Add option UI toggle for smooth transition feature
- Precalculate list of surface colors by turn on first lookup after start/load
- Use precalculated surface color targets for improved performance
- Jump straight to new target color when smooth transitions disabled

Version 3.0:
- switched from IPart-based design to a Harmony patch on XRL.World.Zone.Render()
-- avoids save game compatibility and mod remove/disable issues
-- avoids the need to explicitly disable serialization of fields
-- hopefully results in 1:1 correlation between callbacks and effective ability to apply color updates
- replace thinworld->JoppaWorld long callback delay protection with a more generic implementation that doesn't count any callback delays of >100ms towards smooth transition progress, due to discovery of additional potential cases
- lower night brightness to 75% and sunrise/sunset brightness to 87.5%
- apply brightness adjustments to table colors during class initialization instead of on every surface-level dynamic color calculation
- simplify indexing logic by hard-coding indexes, fixing potential wraparound bug
- restart smooth transition from current point if target color changes, fixing issues with repeatedly entering/exiting dungeons quickly
- throw exceptions for out of range values to aid in debugging
- simplify color finalization code
- always recalculate color if currently at default, fixing potentially getting stuck at default in some cases
- don't recalculate underground brightness unless depth changes or default color is set
- abort transition on reset to default color
- rearrange smooth transition logic to update stopwatch and apply transitional color *before* calculating next target color
- general cleanup/tweaks

Version 2.1:
- add a kludge to make old saves work with the new code changes

Version 2.0:
- use render callbacks instead of event handlers for realtime effects
- implement smooth realtime transitions between color targets (mainly for depth transitions)
- make underground colors one level darker
- set default color game end (fixes background left in weird state on abandon, and background set to default on save without quit)
- set default color on scoreboard show (better handling of thinworld sequence)
- move code to mod-specific namespace
- tons of code cleanup
- add manifest.json for nicer mod list display

Fixed "thin world" freeze by adding code to keep reverse color lookup table updated.

Changed to a new event handling scheme in order to handle more events.

Added code to revert to default background color on death, save, and leaving "Joppa world" (e.g. going to "thin world").