When BluetoothApplet::show-full-menu property is notified (when you
switch from a disabled adapter / no adapter to an active one), we
would show all the menu, including the device separator, without
checking if any devices actually existed.
https://bugzilla.gnome.org/show_bug.cgi?id=637690
When receiving a "devices-changed" signal from BluetoothApplet,
check if some device item corresponds to an existing one, destroy
the remaining and add the new ones.
With this patch, signal emission when no device actually changed
(which happen due to bluetoothd creating temporary devices) result
in a no-op.
https://bugzilla.gnome.org/show_bug.cgi?id=637690
Kill one separator by merging all global actions items at the end
of the menu, which ends up divided in three sections: status,
devices and actions.
https://bugzilla.gnome.org/show_bug.cgi?id=637690
