display a helpful message instead of a NaN time for Classic Quizzes
display a helpful message instead of a NaN time for Classic Quizzes

refs QO-679
flag=none

test plan:
 - if the timer would have displayed "NaN Minutes, NaN Seconds"
   now it should display a helpful message instead
 - the message should be in red (meeting 4.5:1 contrast)
 - when the message is displayed, the timer label "Time Running"
   should be hidden, as should the "hide" button
 - when there are no issues with the timer, it should display
   as before

Change-Id: I33938b0b5208d9d37aab57379459f076086983d3
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/250884
Reviewed-by: Stephen Kacsmark <90aaf30f5583a54f0f3cdbd115e37bda3a251932@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Mark McDermott <20dd8ba615f2257ea7254f93d6f30ae11aa4f904@instructure.com>
Product-Review: Matthew Goodwin <7c47e89894930304a2cdfa1d2ccca1e1eddb893d@instructure.com>

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