Port implicit default content items to use contentItem: property (and improve layout)
See also frameworks/kirigami!1338 (merged) and frameworks/kirigami!1340 (closed)
SettingsPageScanning:
- Improve delegate's layout, port to required properties
- Move "Add" button to the top, fix potential overflows
All items need be limited in width, so that they wrap instead of clipping.
CC @sitter