Make the group dialog work in Qt5
Build, open kreportexample and add/edit/remove group sections
- Fix dialog margins (shall be like in Help->About Kexi for example), to do this just reset values of the layout*Margin properties in Designer for the DetailGroupSectionDialog widget
- Base branch for this patch shall be 3.0. Then we would merge to master.
- Extra: set buddy for the three check boxes (clicking on the labels is still broken even if you set StrongFocus for them but this may be due to the issue with Breeze style)