Fix AmbiguousForeignKeysError in models.py
Fix AmbiguousForeignKeysError in models.py

Also removed back_populates tags from User and Question classes relationship()-calls. They were giving me trouble and I'm not sure how to do them properly.

LauriKauhanen/calm-temple-8514,LauriKauhanen/calm-temple-8514,LauriKauhanen/calm-temple-8514