Really temp commit. trying to resolve a db migration issue
A stab should be conneted to a subpart - not a whole question

Given that
  1. each stab has an associated scan AND
  2. the whole solution => stabs at all subparts could span multiple scans

it makes sense to bind stabs to subparts instead of questions.

Also, note that even though we can reasonably expect(require) stabs
at puzzles to be only 1-sheet long, we cannot make the same assumption(demand)
of questions