Make "View Grades" page responsive
Make "View Grades" page responsive

closes EVAL-1032
flag=none

Test plan:
- Open the grades page (/grades) for a student or teacher
- Set your browser to responsive mode, and reduce the width of the page
  to 320px
- The contents of the page should now be displayed in a single column
  and not stretch past the width of the window

Change-Id: Ib852e0fbf888a86372e184f78d7a13d6f981ff35
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/249596
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>
Reviewed-by: Gary Mei <4dff5ebcff9ed76793b70b9470ac64791a16ed11@instructure.com>
QA-Review: Kai Bjorkman <4693b3d9e71784d629732770ab5e83ed8fbdb83e@instructure.com>
Product-Review: Daniel Sasaki <ae19fabf7fe19dff310008c9b6a4d2ec84d311d8@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms