Ember Quiz Stats [+Backend] - Numerical

Adds numerical question support to CanvasQuizStatistics and the renderer
in the Ember quiz statistics (subclass of ShortAnswer question).

Closes CNVS-13087, CNVS-13086

TEST PLAN
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  - create a quiz with a numerical question:
    - mix and match between the answer types: exact, exact with margin,
      and range answers
  - take the quiz by a number of students, we need to score like this to
    cover the possible cases:
    - a correct answer
    - a missing answer
    - an incorrect/out-of-range answer
  - hitting the stats api should return the documented metrics in the
    output of "question_statistics":
    /api/v1/courses/:course_id/quizzes/:quiz_id/statistics [GET]
  - visiting ember quizzes should now render the numerical stats which
    is similar to short answer (fill in the blank) and multiple answers:
    - make sure the "Other" and "No Answer" answers and bars show up
  - verify the API docs are updated

Change-Id: I0c9ec0dbc7c729410241177b6ed43b0cd4dad143
Reviewed-on: https://gerrit.instructure.com/35431
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>