!nextmeetings command

[ryanlerch]

IRC zodbot had two commands !nextmeetings and !nextmeeting that we should implement here.

both queried fedocal and returned the next scheduled meetings.

• !nextmeeting showed the next meeting (1) for the room that the command was called in
• !nextmeetings showed the next 3 meetings across all rooms.

IMHO we should just distill this down into a single !nextmeetings command that shows the next 3 meetings everywhere, and the next meeting in the current room (if a meeting is scheduled in the current room)