Accessibility: assignment names and Total are read in Assignments Settings

Fixes CNVS-13099 CNVS-13100

Test plan:
- Using a screen reader, visit assignments, and open the settings cog.
- Check the "Weight final grade based on assignment groups" control.
- Verify that when navigating down the right column of the table with a screen
  reader, that the label for each field, the value in the left column, is read.

Change-Id: I528bf4a377e297cd4e683d25c50145ace6fce3d1
Reviewed-on: https://gerrit.instructure.com/36688
Reviewed-by: Cameron Matheson <cameron@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Aaron Cannon <acannon@instructure.com>