📜 adds paper workbook format and code to generate workbooks

[Felienne]

This PR adds new paper worksheets for all levels, for now only in Dutch since I am trying them out in class. It features a small YAML format to describe question types to ease later prettifying of the sheets.

Not all it ready yet, this is a TODO for myself:

• Number exercises so they will always be correct
• Teacher explanations and answers still need to be generated
• Translation features, of course
• When we have En content, add this folder to Weblate and format correctly
• Automatic generation of PDFs (I now use Typora)
• Arrange syntax highlighting (complex!)
• Add error message questions!

[mergify[bot]]

Thank you for contributing! Your pull request is now going on the merge train (choo choo! Do not click update from main anymore, and be sure to allow changes to be pushed to your fork).