Implement Message Tracking

[JakenVeina]

Should probably discuss with staff whether this is a priority, since other bots accomplish this at the moment. But I'd like to get it implemented eventually, either way.

This involves tracking the creation (and editing) and deletion of messages, in support of user statistics.

Message content is NOT to be stored. AT MOST store a hash value of the content, so duplicate messages can be detected (probably don't REALLY need this).

Will we still need a "participation" designation, for channels?

Consider pruning the main table to a 30-day history, and either dropping older records entirely, or at least moving them over to an archive table. Need to discuss the real needs of this system.