Color contrast - Individual rubric view

fixes CNVS-15649

This replaces the icons we had with color corrected ones so we
meet our contrast ratios for accessibility.

Test Plan:

- If you don't have any, navigate to your Rubrics page and add one
- Attach a Module outcome to a rubric and then view your Rubric
page
- There should now be a little flag that appears on it which should
meet our ratio

Reference screen: http://cl.ly/image/1j1E2l001O3A

Change-Id: Ie18ecd335fd350c4be6eda6845ebb17be7da71cb
Reviewed-on: https://gerrit.instructure.com/45365
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Chris Hart <chart@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Colleen Palmer <colleen@instructure.com>