System to mark people as "Category Expert"

[Josh-00FF00]

I think it'd be nice to have "subteams" of people we can request help from. For example, altering all pwn-ers when a new challenge pops up

!category alert pwners <msg> # Send message to all pwners

!category markme pwner # Add to mention list
!category unmarkme pwner # Remove from mention list
!category show # Show everyone's membership

Or smth similar