Ember Quiz Stats - FITB & Multiple-Answer

This patch adds two new renderable question statistics to the new Ember
quiz stats page: fill in the blank (short_answer) and multiple-answer
ones.

They are very similar to Multiple-Choice questions except there's no
discrimination index, and the correct response ratio is calculated a bit
differently in the case of multiple-answers.

Closes CNVS-12987

TEST PLAN
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  - like the other stats tickets, create a quiz with those question
    types and take it by a number of students
  - verify the first donut chart that shows the student ratio displays
    proper data:
    - in case FITB: it's the same as multiple choice and T/F
    - in case of multiple-answer questions: only the students who have
      fully answered the question correctly should count in the donut
      chart (e.g, if you picked two answers, one correct and one not,
      that student shouldn't count)
  - verify that in the second chart, the bar one, all correct answers
    are highlighted in light green and not only the first one (as is the
    case with MChoice)

Change-Id: I3b7160417166cc57afa912a41f4ff04d309a8cfd
Reviewed-on: https://gerrit.instructure.com/34689
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>