DerFrZocker authored and md_5 committed 7983b966630
#1029: Trial changing a small number of inner enums to classes/interfaces to better support custom values
This PR is a subset of the enum PR #660 and is designed as a low impact
trial run of the design and backwards compatibility to inform subsequent
development.
Additional plugin compatibility features may be available by setting
`settings.compatibility.enum-compatibility-mode` to `true` in
`bukkit.yml`.
