Improve status bar handling on mobile devices

[voltangle]

For iOS, I can use the apple-mobile-app-status-bar-style=black-translucent meta value to make it extend under the notch, and use some safe area to make the content not go under the notch.
For Android, I'll have to patch (and later submit a PR to) Citizen to add support for different theme colors (via theme-color meta value) for different, well, themes. Citizen only supports one value for both themes.
If the iOS stuff will not work out, it's fine, at least it will just use the theme-color meta value.