Version 4.2.4

- [CardDAV] vCard LABELs are not generated anymore - now there's only the structured address
- [CardDAV] better support for read-only address books (make contacts "really" read-only as good as possible)
- [CalDAV] handle a rare exception when a time zone is known to Android but not to ical4j
- [UI] use Material switches for preferences
- [UI] use switches instead of checkboxes in accounts so that it is more understandable what should be synchronized
- [UI] add monochrome/themed icon
- [UI] added some pre-set base URLs
- [UI] updated Manual URL (the manual is now automatically updated by Github Actions after editing it)
- [jtx Board] remove filesize restriction for attachments
- improved compatibility (especially HUAWEI to display DAVx5 calendars there again)
- fix a bug that caused the account view to be empty after renaming an account
- fix a crash when accounts vanish somehow
- new languages (thanks to our translators!)