CQS: FITB and friends

Adds question statistics for Fill in The Blank, Multiple-Answers, and
Numerical questions.

Closes CNVS-15213

TEST PLAN
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  - create a quiz with the questions above
  - take the quiz by at least two students
  - visit statistics_cqs page
  - verify the question types above render and show the correct-answer
    donut chart, as well as the answer distribution chart (like
    MChoice)

Change-Id: I4d1b2653fe8806e51ec784a507fe6dc99d2cb51b
Reviewed-on: https://gerrit.instructure.com/40361
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ryan Taylor <rtaylor@instructure.com>
QA-Review: Trevor deHaan <tdehaan@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>