Ember Quiz Stats - FIMB & MDropdowns - "No Answer"

Add support to display the "No Answer" and "Other Answers" (FIMB-only)
in the answer bar chart for those question types, and make the bars
visible for answers with 0% responses.

Totally unrelated change: now using the icons Blake made for us.

Closes CNVS-13033, CNVS-13071, CNVS-12961

TEST PLAN
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  - create a quiz with FIMB and MDropdowns questions
  - take the quiz by a number of students and type in different answers
  - make an API request to stats:
    GET /api/v1/courses/:course_id/quizzes/:quiz_id/statistics
    - verify you get the documented metrics and they have the proper
      values
  - visit the ember quizzes page and verify that:
    - the charts are still working
    - the bar chart now displays a bar for "No Answer" responses and
      another bar for "Other answers" if your students provided any
      (only applies to FIMB questions)
  - new bar/tooltip improvement: answers that have 0% now take up at
    least 5 pixels of the chart so that you can hover over them and get
    the tooltip to show, earlier it was really difficult because they
    were too tiny

Change-Id: Ie9a7ea6bb539fa9d120679997d4a20737f8ad03c
Reviewed-on: https://gerrit.instructure.com/34953
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>