Added a mob cleaner
Running it will clear all inactive mobs of a certain type in a given world
Commands:
	/clean world
		Clears all mobs defined in the config for that world
Permissions:
	cleaner.clean
		Allows use of the /clean command
	cleaner.clean.<world>
		Allows use of clearing world <world>
	cleaner.clean.*
		Allows cleaning of any world
Settings:
	clean:mobs-to-clean
		A list of which mobs to clean from that world
		e.g
		-Enderman
		-Skeleton
		-SnowMan
Translations:
	cleaner:clean-world-no-perm
		The message for no permission to clean a specific world
	cleaner:clean-world-cleaned
		The message for successfully cleaning a world