ember quiz show - moderate displays due at

add a due at column to the moderate ui table. shows the specific due at
date time for a given user / submission on a quiz.

closes CNVS-13151

test plan:
  - enable ember quizzes
  - build quiz with time-limit
    - as student, begin taking quiz
    - in another tab as instructor, reload / refresh table
    - due at column should display time when their submission is due
    - current time should count down to the time limit
  - build quiz with due date
    - as student, begin taking quiz
    - in another tab as instructor, reload / refresh table
    - due at column should display the due date for their section
    - current time will count up with the duration the submission is
      open
  - build quiz with lock at date, and expired due date
    - as student, begin taking a quiz
    - in another tab as instructor, reload / refresh table
    - due at column should display the lock at date
    - current time will count up with the duration the submission is
      open
  - build quiz with no time-limit, no due date, no lock date
    - as student begin taking quiz
    - in another tab as instructor, reload / refresh table
    - no due at data should appear in column
    - current time will count up with the duration the submission is
      open
  - build quiz with time-limit set to 30 minutes, Due Date set 5 mins from
    now, Lock Date does not matter
      - as student begin taking quiz
      - in another tab as instructor, reload / refresh table
      - due at column should display the due date for their section
      - current time should count down to the due date
   - build quiz with time-limit set to 30 minutes, Due Date is expired,
     Lock Date set 5 mins from now
      - as student begin taking quiz
      - in another tab as instructor, reload / refresh table
      - due at column should display the lock date for their section
      - current time should count down to the lock date

Change-Id: I4097d858747a99ce03b40bf4542377206209d136
Reviewed-on: https://gerrit.instructure.com/35211
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Jason Madsen <jmadsen@instructure.com>