Keyboard shortcuts for grouping, overlays and preferences.
Darktable 2.0.4 @ Fedora 23 on x86_64.
Image grouping may be turned on/off only by mouse click on [G] button in the top panel. It would be nice to have a (configurable) keyboard shortcut for it.
The same for image overlays (star button right to [G] button) and preferences (gear button right to star button).