ember quizzes: sort quiz index page by dueAt then title

Test plan:
  - As a teacher, create a bunch of quizzes with different names and due
  dates.
  - They should sort by due date (if there's no due date, it should
    come before AFTER stuff with due dates), then by title.

closes CNVS-12432

Change-Id: I82d18577d0a18061a7853526a93990b202f7aa5f
Reviewed-on: https://gerrit.instructure.com/33963
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>