Refactor css

[HendrikSchmidt]

This PR does a bunch of things to refactor our CSS:

• Updates Angie with some minor changes to typography, shouldn't be visible
  • Use default responsive header styling from Angie instead of our own
• Creates a custom twMerge() that works with ds- classes
  • Adds an EsLint rule that prevents importing the default implementation
• Styles lists ul and ol per default and removes those styles for exceptions
  • They get list-disc/list-decimal, pl-24 and max-w-prose
  • This styling is removed by using the newly introduced list-unstyled class
• Removes support for IE11, "old" Safari and browser that don't support focus-visible
• Refactors styles.css to mostly use tailwind @apply instead of native css
• Inlines styles wherever possible
  • details / summary / Accordion styling
  • Inlines DiTo specific styles.css or moves them to shared/styles.css
  • footer links
  • PreCheckNavigation shift prevention
  • ParagraphList lists styling
• Removes the following classes
  • rich-text (inlined)
  • text-link-white (replaced by styling .text-white .text-link now)
  • rich-text-2xl (unused)
  • sr-only (implemented by tailwind)
  • paragraph-list (inlined)
• Refactors principle section on landing page to simplify logic

Includes some miscellaneous fixes that I happened to stumble across.

[mpanne]

Love it! Thanks for the effort! ❤️