* Added a 'RDAIRPLAY.MESSAGE_WIDGET_URL' field to the database.
* Incremented the database version to 374.
* Added 'RDAirPlayConf::messageWidgetUrl()' and
'RDAirPlayConf::setMessageWidgetUrl()' methods.
* Modified rdairplay(1) to make the Message Widget retain the loaded
URL across instances.
* Modified rdairplay(1) to make the Message Widget continually poll
and update loaded URLs using the 'file:' schema.
Signed-off-by: Fred Gleason <fredg@paravelsystems.com>