/mc command group

[andrewj-brown]

We now have /mcwhitelist and /mcadmin run and /mcunwhitelist. These should all be placed under the umbrella of one (1) command group, instead of being different commands.

Additionally, more functionality:

• allowing non-admin users to unwhitelist themselves (or maybe this is a feature? only letting admins remove your entries from the whitelist means no account-switching shenanigans)
• allowing you to see which user you currently have whitelisted
• allowing admins to prevent someone from whitelisting an account
• allowing admins to link admin-whitelist entries with accounts so people who've been admin-whitelisted don't get a 2nd go at the whitelist

[JamesDearlove]

My very rare "appearing for 2 cents moment": as you cant restrict commands in a command group, i think splitting into minecraft and mcadmin might be a better solution