[Observium] Maintenance and down devices

I've made a small change to change how down devices are displayed when in maintenance mode that seems generally useful enough to include in the distro. It scratches my itch of being able to quickly see what downed devices have scheduled maintenace. It would probably be useful to extend to more areas like the color of device links and other entities.

In html/includes/print/status.inc.php (about line 66):

if (isset($GLOBALS['cache']['maint']['device'][$device['device_id']])) $string .= ' <td><span class="label label-info">Device Down (Maintenance)</span></td>' . PHP_EOL; else $string .= ' <td><span class="label label-important">Device Down</span></td>' . PHP_EOL;

Jesse