Display "Working..." notification in same style as used in exports
In some images the notification "Working..." is hard to see.
The notifications that are used for exports are very well visible, so I suggest using the same code to display all notifications within darktable.
How about an option to use system's notification library? It would be nice to have ubuntu's (kde's, whatever's, ...) notifications pop up for exports et al. - No need to reinvent the wheel.