Add a command that revokes all group invites

[awoo-civ]

There's no way for players to tell who is invited to their groups which makes lingering invites potentially
dangerous.

[ProgrammerDan]

Hmm, I thought for sure there was something in the GUI to show this. Been a while.

[awoo-civ]

@ProgrammerDan Oh you're right. There is and it works. I just assumed nothing was there since it's not a command.

[ProgrammerDan]

Oh, whew, ok. I'll leave this open though, but that does reduce the severity; some folks prefer to just use commands instead of walking the GUI so it's a valid feature ask.