Upstream changes
- Merge branch 'navigator-offline' into 'master'
- check if backend is reachable when handling night mode change instead of relying on navigator.onLine
- Merge branch 'weblate-integration' into 'master'
- Translated using Weblate (Latvian)
- Translated using Weblate (Latvian)
- Merge branch 'fix-youtube-nocookie' into 'master'
- Fix youtube-nocookie support
- Merge branch 'configurable-default-themes' into 'master'
- drop unused legacy (?) handler method OPML->import()
- add necessary plumbing for auto light/dark switch for the forgotpass handler
- make default light/dark themes configurable, add support for main application and login form