Quiz Stats - Multiple Answers

Ports the generation of stats for that question type to the CQS gem.

Changes:

  - no longer exposing "user_ids"
  - can now identify students who skipped the question

Closes CNVS-13089

TEST PLAN
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  - create a quiz with multiple-answer question(s)
  - take it by a number of students and cover the following cases:
    - answer correctly by picking only the right choices
    - answer almost correctly by:
      1. picking only 1 right choice
      2. picking 1 right and 1 wrong choices
      3. picking everything
    - answer incorrectly by picking only the incorrect choice(s)
    - don't answer at all
  - get the stats from the API:
    - for "responses", "correct", and "partially_correct", verify they
      meet the specification in the docs
      - also for the "responses" field in each document in "answers"
    - verify that there is an answer document with "none" for an id with
      "responses" that reflect the number of students that skipped the
      question
  - visit ember quiz stats:
    - verify the "Attempts: X out of Y" should read the "responses"
      field out of the total quiz participant count
    - verify the donut chart reads the correct "correct" response ratio
    - verify there is a "No-Answer" bar
    - expand the question details:
      - verify that all the choices are displayed, and the correct
        choices are highlighted in GREEEN

Change-Id: Ibc08b6f521f9cae35dd16950c68c164d7e27d95d
Reviewed-on: https://gerrit.instructure.com/35736
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>