lists.dragonflybsd.org main page update

[Justin Sherrill]

The old mailarchive for @dragonflybsd.org mailing lists had a main
page that listed all active months on a mailing list by thread or
date.  Now that we've switched to Mailman, it doesn't have a "main
page" listing like that as part of the normal setup.

I recreated that page, but pointing at the appropriate Mailman lists.
It's at http://lists.dragonflybsd.org/ and replaces the old location
of http://leaf.dragonflybsd.org/mailarchive/ - this should be easier
to remember.