srgb - fix total grade rendering logic and i18n issue

fixes CNVS-14153

test plan:
  - go to srgb with weighted assignment groups
    - final grade points ratio should never
      show up (e.g. "90/100 points")
  - go to srgb with unweighted assignment groups
    - final grade points ration should
      show up (e.g. "90/100 points")
      if the student has a grade
    - changing a grade should update the ratio
    - changing students shouldn't break the ratio
    - students without graded assingmnets
      don't break the ratio

Change-Id: I052f8ba54360e501422cdc354f9760306e457dbe
Reviewed-on: https://gerrit.instructure.com/37524
QA-Review: Amber Taniuchi <amber@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>