https://github.com/BentoBoxWorld/Level/issues/229
First, the top ten tables are never actually used or loaded. They are
created in memory by loading the island levels. So there is no reason to
keep saving them.
Second, the island level data is saved every time it is changed, so
there is no need to save all of the cache on exit.
* Stores level data on a per island basis
* Migrate after BentoBox worlds have loaded.
* Added new Admin set initial level handicap command
* Bug fixing
* Fix test
* Removed code smell
