Support autojoin by group

The staffAutojoin feature can now be used to conditionally set
autojoin for specific group symbols. If room.staffAutojoin is a
string (set it in .chatRoomData and restart the server), groups
whose symbols are in the string will autojoin that room.
Remove the /report command

According to reports, it's only ever been used for trolling, and the
Help room does what it's trying to do in a much better way.