Finer permissions for world properties and commands.

[ELLIOTTCABLE]

There's some world-properties I'd like one rank to be able to set, without giving them full access to world-modification. (Specifically, stuff like difficulty, hunger, PVP, and weather … without them changing the seed, portal-forming rules, environment, or anything else truly catastrophic.)

It'd be nice to have the availability of granular permissions for changing the various world properties in-game. At the moment, I can granularly control multiverse.core.gamerule.set, but not anything to do with difficulty, which is annoying. (=

[main--]

Good idea, we can implement per-property permissions in MV3.