BQM : add new signal to dispatch busy state to AlbumGUI, to disable BQM action...

BQM : add new signal to dispatch busy state to AlbumGUI, to disable BQM action from GUI when it's busy.
BQM cannot handle new item when processing is under progress, because it process all current queues as well.
If new one is add in list, this can crash application.
BUGS: 283281