Ender leash fixes and improvements
- Max health of animal is now stored (important for horses)
- Donkey chest inventory is now preserved
- Animal owner UUID (if it exists) is now preserved
- Added permission node to control if players can leash animals owned by someone else
- If animal is leashed when captured, leash is now dropped.  Additionally, only animals hitched to a post can be leash; if any other entity is holding the leash, capturing will fail.
Changes to creative mode & ender inventory interaction
Added "creative_inventory_access" config setting, default false
Added "stb.enderaccess.creative" perm node, default op only
By default, creative mode players may not interact with an ender inventory (bag or box) any more.
In addition, we hook Multiverse and if the world is marked as creative, item routers in that world (sender/sorter/distributor) will no longer be able to insert modules into an ender box.