Merge bukkit utils into main repository

[minoneer]

Merges https://github.com/uskyblock/bukkit-utils into the main repository as a separate maven module.

This has many advantages:

• It is easy to keep spigot/bukkit versions in sync
• The two are tightly integrated, and therefore development is much more streamelined
• Logically, they both belong to the same project as neither exists without the other
• bukkit utils depends on po utils, which are already merged into the main plugin. We therefore have a cyclic dependency between projects.
• It is easy to see which parts of bukkit-utils are still in use, and which are redundant and can be removed

Note: this merge should compile, but is untested. Merging the 1.20.6 update #55, which depends on this merge, will result in a runnable plugin.

[Muspah]

LGTM, thanks for all the wonderful effort! <3