DA - quizzes

fixes CNVS-14094

test plan:
  - course with DA as students and teacher
    - api show & index
    - quizzes index page shows only assigned quizzes
    - quizzes show page url redirects to index if
      quiz isnt visible to user
    - grade calculation
    - gradebook/grades page
    - calendar events events
    - modules filter out quizzes correctly
    - observers see same things as their students
    - if a student takes a quiz and it is not graded and then
      loses visibility, make sure that the GB greys out the cell
      rather than showing a submission icon
  - same course with DA off works normally

Change-Id: I10b936f1516d6d24f11d74c0bb572051f0b1d1c4
Reviewed-on: https://gerrit.instructure.com/39897
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Mike Nomitch <mnomitch@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Mike Nomitch <mnomitch@instructure.com>