Warn groups when their president is not on the officers' list

[adehnert]

I'm not sure what exactly this looks like, but it seems reasonable to (do the moral equivalent of) blanche or blanche -r each groups' officers' list every night, and warn if it stops containing the group presidents. We routinely get people who seem to remember to update the ASA DB but not the officers' list, and this seems like it might help.