[Players] Go to Sleep Player Coordination / Who's in which world?

When chauve and friends were trying to round up everyone to go to bed, there was a lot of "okay, who's in this world" "who's sleeping" and I was thinking about /mv who, and how it shows a breakdown of who's in what world.

Perhaps either give folks the permissions to use it, or maybe add an option to your own /list command. Iunno.
