Fix lint warnings

See merge request zesje/zesje!157

Allow for creating feedback in the exam view

Closes #8

See merge request zesje/zesje!141

It's only necessary in the exam view, as the approach in the grade view
is different

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

Fix error while exporting with no students

Closes #318

See merge request zesje/zesje!156

Add redis dump, submissions test folder to gitignore

See merge request zesje/zesje!154

 - Remove panel from EditPanel/FeedbackBlock, must be left to
 implementer to use it where needed (not in Exam.jsx, for example)
 - Removed is-active from feedback option blocks
 - Add text saying that the section below it shows feedback options

This still crashes on problem deletion, but fixes regular use.
You can also switch exams and everything.

This is a sub-optimal fix, could be adjusted later on.

Fix the corner marker detection tests

Closes #314

See merge request zesje/zesje!153

Fix unable to save feedback with score 0

Closes #199

See merge request zesje/zesje!151

Set scan processing status while waiting for a worker

See merge request zesje/zesje!149

Add scaling arguments to celery for yarn dev

See merge request zesje/zesje!148