New: tap About in Settings for a compact dialog with the version, credits, licence and contact.

Fixes from the F-Droid review:
- The APK contents list was unreadable in dark theme.
- Split apps saved as "name.apks.apk" instead of "name.apks". The archive itself was always correct.
- Settings could not be scrolled, so the About card was unreachable.
- System bar icons ignored the in-app theme.
