Revamp UI to change it from multi-tab-UI with radio buttons to a single page KCM with combobox
So far, first steps make the CfgPlugin have a combobox based UI :
Depending on bug fix : D26690
Main UI refactoring: D26797
Add maybe other default apps : video, audio, calendar and image
Reference : gnome code https://gitlab.gnome.org/GNOME/gnome-control-center/blob/master/panels/default-apps/cc-default-apps-panel.c#L155
Then merge them into a single page.
First complete UI prototype :