Add open questions to the quiz

[Felienne]

Our quiz now only has multiple choice questions, which is nice since we can easily verify them, but we are missing out on some interesting open questions!

I would love to explore doing this, here are a few steps to take and things to consider:

1. Simple add questions with an open text field, with no grading at all.

This is lovely for questions that we can learn from! Like: "explain this concept in your own words", or "what was the hardest part of this lesson?" We would still need to a) add the questions to the UI and b) save answers into the database, probably requiring some changes to the tables

2. Allow teachers to grade open answers

A next step could be to show the open answers to teachers so that they can verify them.