Apply black before refactoring

[rrhg]

Describe your changes

1. clean_mudule.basic_clean(nb_path) already implements this logic of applying black
2. So now is also run before export.refactor(...) (in cli.py)
3. I can work on the failing tests. First would like your input, I could be missing something.

Issue ticket number and link

Closes #84

Checklist before requesting a review

• [ ] I have performed a self-review of my code
• [ ] I have added thorough tests (when necessary).
• [ ] I have added the right documentation (when needed). Product update? If yes, write one line about this update.