Possible enhancement over stock Bucket: Log who taught each factoid

[dgw]

This came up in chat for me tonight where my "real" (Perl-based) Bucket bot hangs out, and we were trying to figure out who might've added some of the ancient factoids from probably a decade ago.

Downside is that this feature couldn't possibly fill in an existing database retroactively, unless someone wants to get really enterprising with a logfile parser (since a Bucket bot's log channel might itself be logged somewhere). But I think it's worth thinking about the utility for new installs, or newly added factoids.