Finalize the Great Translation Purge

• waits for !1663 (merged)
• closes #238 (closed)
• closes &7 (closed) 🎉

What does this MR do?

• finish translation-refactoring: Settings* and the very basics of Report*/Quiz*
• replace hardcoded role logic with new getRoleName helper
• remove all PHP translations! and associated infrastructure
  • this includes moving all implicit form-field translations to YAML
• update i18n devdocs

How confident are you it won't break things if deployed?

Much to my surprise, the build for this is green. It would be pretty good to test the changes through and through, since it's related to core functionality (displaying text)

How to test

Basically: do things and check if the text you are seeing is what you expected. A lot. 💩

Checklist

• no added functionality that wasn't already covered by tests
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in Beta Testing Repo:
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...). how this change can be tested.
  • Be aware, that also non technical people should understand.