hook up extension checkboxes for ember quizzes moderate page

fixes CNVS-12450

test plan:
  - as a teacher
  - enable fabulous quizzes
  - enroll a few students in the course

  - create a quiz with both a time limit and a limited number of attempts
    - visit the quiz moderate page
    - click the "edit" icon for a student
    - the modal dialog should continue to work as described in g/35089

    - use the checkboxes to select multiple students at once.
      - clicking the header row checkbox should toggle selection of all checkboxes
      - deselecting all student checkboxes should automatically deselect the header one
    - after making a selection with the checkboxes - a new link appears to
      change extensions for the selected students
    - click this link to bring up the extensions modal dialog
    - make sure that changing the extensions from here updates the
      extensions for all selected students.

  - there is also a new "unlocked" icon that shows up when you set the
    manually unlocked status for a student. make sure that when this setting
    is updated that the lock icon appears.

Change-Id: Ibc55087a99d02fe3da7f9390e07a1f0bb5ccca35
Reviewed-on: https://gerrit.instructure.com/35228
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ahmad Amireh <ahmad@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>