Issue #29: Implemented an offline maintenance page

I basically copied/pasted the source from our "maintenance mode"
page into the maintenance-page--offline.tpl.php page and adjusted
the title and message, accordingly. This way, at least some
explanation will be given to site visitors if the database is
being problematic, rather than a slew of unfriendly drupal error
messages.

Signed-off-by: Elliot Voris <elliotfriend@gmail.com>