This was only used to start the default media player on gnome-settings-daemon,
when the user presses the Media key. We just open the default for audio/ogg
there, so no need to ask the user for a default media player
When the theme or screen changes, we need to make sure that
the previous handler for the theme-changed signal is disconnected
to avoid the callback being called when the panel has been unloaded.
https://bugzilla.redhat.com/show_bug.cgi?id=610289
