* Restore the details dialog dock position if it was previously docked (i.e. not floating).
* Since the details_dialog instance was not deleted after closing by default, the previous instances were still saving their own geometry. We now delete them explicitely if we have to recreate a new instance to avoid the signal triggering the callback to save the geometry.
* Since restoreGeometry() and saveGeometry() are only called in our QDockWidget, it should be safe to modify the methods for the Preferences class (in qtlib).