Upgrade to newest quiz parser/quiz format

It turns out I never upgraded the quiz-parser version the quiz was using, especially after the upgrades in 2018. It’s still using:

gem 'quiz', github: 'dtu-compute/dtu-quiz-parser', branch: '2016', tag: ‘0.3'

As far as I know there are no negative consequences to this — there aren’t issues with the quiz parser as far as I know — but it does mean there needs to be a transition. Going through the tests there are at least some breaking changes.

That being the case, it probably doesn’t make sense to update that in phase 0. Maybe in phase N, when we replace the MongoDB and there is no carry-over quizzes from the previous DB would be a better time.

For now I’ll revert back to the older version, unless you prefer otherwise.

[note that this might well just be subsumed into a new version that encompasses the new AsciiDoc version of the combined website/quiz syntax]