Support connect to multiple channels and last-seen message marking.

Support connect to multiple channels and last-seen message marking.

When connecting or reconnecting we can join a number of channels and
we need to re-join all channels on a reconnect.

When a tab is hidden and new messages are received place a marker and also
handle alert regexps with a bright background and a tab icon if someone
addresses me or mentions something I care about.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>