Merge branch 'feature/pre-grading' of ssh://gitlab.kwant-project.org:443/works-on-my-machine/zesje into feature/pre-grading

Merge branch 'develop' of https://gitlab.kwant-project.org/works-on-my-machine/zesje into feature/pre-grading

Rewritten doc, update_database returns submission and exam, pregrading now checks for specific submission

Changed commented out code back, changed the way errors are printed, added temporary fix for box check, feedback description should be the label of the mc_option if it is present

Merge branch 'combinatory-fixes' of https://gitlab.kwant-project.org/works-on-my-machine/zesje into feature/pre-grading