Inline Analytics

  Display of answer distribution graphics inline on the problem page
  for instructors.

  Problem types supported for graphics:
    - MultipleChoiceResponse
    - ChoiceResponse

  Problem types supported for line item display:
    - OptionResponse
    - NumericalResponse
    - StringResponse
    - FormulaResponse
    via setting

Internal review only for now.
Looking at the structure of this function, I strongly suspect that what would helped this code be cleaner is to build a generator into Capa (meaning in that library) that yields a NamedTuple that basically returns all of the groups of a response, but also carries  the response_type and whatever other data you need to filter.

I'm not going to require it for MVP, but I'd like to see it before the upstream PR.