QuizStatistics API

Closes CNVS-8989

CHANGES
-------

  - ItemAnalysis can now be generated to a Hash as well as CSV

TEST PLAN
---- ----

  - create a quiz with a number of questions (true/false and
    multiple-choice a must-have)
  - take the quiz by 2-3 students
  - perform an API request as described below and verify that you get a
    statistics object that matches the API docs
  - do it once in legacy JSON format, e.g:
    "Accept: application/json"
  - do it once in JSON-API format, e.g:
    "Accept: application/vnd.api+json"
  - read the API docs and report any mistakes or stuff that's not clear,
    the stuff is written in the QuizStatistics module

Endpoint: [GET] /api/v1/courses/:course_id/quizzes/:quiz_id/statistics

Change-Id: I1588e1cdc8955b890c739df4c730507dad7118d1
Reviewed-on: https://gerrit.instructure.com/31141
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>