Re-add Spigot compatibility

[Jikoo]

• Re-added Spigot support
  • The full PlanarEnchanting release offers first class Spigot and Paper support.
• Fixes potential incompatibility with max stack changing plugins
• Fixes default config containing invalid enchantability category
• Improved some unit tests (some are still a mess, I just don't have it in me to rewrite them all more properly rather than fix the glaring failures)

[Jikoo]

Issues so far:

• Both:
  • Silk does not pause when result is full
  • Something is wrong with prior work handling.
  • Conflicts (and other complex settings) don't load on first run.
• Spigot:
  • Stacks still can overflow max due to fortune. Unsure if I want to fix this because it prevents losses due to high fortune+efficiency filling furnaces faster than hoppers can remove results. Also unsure if this is Spigot-specific, it's a bit annoying to replicate.
    I have determined that this is a feature, not a bug. I will probably forget I made this determination and encounter it in another couple years only to reach the same conclusion.
  • Spigot bug with applying enchantment hints (and indirectly, with enchanting at all as a result because buttons are disabled)