netsplit handling improvements

[retroj]

It would be nice if the netsplit handler would show in the buffer who was cut in the netsplit. Since a netsplit is indicated by a series of QUITs with (*.net *.split) as the quit message over a period of possibly many seconds, the netsplit handler would need a mechanism to collect the names and report them after a delay. When the first quit comes in, it might say something like "netsplit in progress", then 30 seconds later, or however long, it would report the nicks that have disconnected so far, and continue every 30 seconds until an interval has passed with no disconnects.

[jorgenschaefer]

It should be somewhat easy to start a timer in circe-display-QUIT or circe-netsplit-quit which reports the current state of the netsplit (like /WL does) after a given time.

I'm a bit torn on whether it should be active by default. Probably yes. Happy hacking. :-)