create PermissionsSerializer for serializing permissions

test plan:
  - specs pass
  - You should see a "permissions" object in the quizzes API,
    both when using the JSONAPI version and normal version.
  - In the JSONAPI version, in the "meta" object, there should be
    a "permissions" object with a "create" key. It should be
    "create": true for teachers/admins and "create": false for
    students.

Change-Id: I74f89b41605b369ddb4c2b09e5d5752ce22d5edb
Reviewed-on: https://gerrit.instructure.com/28831
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Myller de Araujo <myller@instructure.com>
Product-Review: Stanley Stuart <stanley@instructure.com>