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.
Perhaps a namedtuple would make this transparently obvious, while also making it convenient to dereference the members later. :)

In general I think tuples are the right thing when you're making collections of things that you don't expect to mutate, which you seem to be doing a lot of. And if you're going to use tuples, my feeling is, you may as well use namedtuples so people can just read their declarations and get a sense of what they're looking at. And so you can refer to their members by name rather than number.