Add a plugin that auto-restarts if channels are too quiet

[zigdon]

Either as a setting, (monitor #xkcd for silence, if nothing said for longer than 10 minutes, restart) or if we want to get fancy, auto-detect what would be a good test (pick the busiest channel, and detect what is an unreasonable silence).

This would help bucket restart after a netsplit where it ends up on an isolated server for whatever reason.

[dgw]

Is it silence in particular, or would it do to monitor for a flood of QUITs that exceeds some percentage of the channel membership? Reacting to 90% of the channel quitting due to a netsplit would be faster than waiting for silence. It's debatable which would be more prone to false positives.