[Feature] Dark mode

[sthewissen]

• [x] Implement dark mode, which is set automatically in the app depending on user settings.
• [x] Add an override in settings, letting the user decide.
• [x] The first tab somehow has a different background color than the others.~
• [x] Controls that the OS colors need explicit colors per theme.~
• [x] The status bar color should be dependent on AppThemeBinding.

[sthewissen]

Issues still in there:

• The first tab somehow has a different background color than the others.~
• Controls that the OS colors need explicit colors per theme.~
• The status bar color should be dependent on AppThemeBinding.

[sthewissen]

Fixed the first one, through setting Translucency to Opaque for the tab bar.