added points v percent toggle to srgb

fixes CNVS-11194

test plan:
  - go to SRGB with unweighted groups
    - The "Show Student Grade Totals as Points" box should be checked depending on current settings
    - if you toggle the checkbox and go to GB2 and/or student summary page, totals should change
    - if you weight assignment groups, in SRGB
      - the check box should disappear
      - totals should go to % in GB2 and grade summary page
      - final grade should not display points/possible points
    - if you unweight assignment groups
      - checkbox should reappear unchecked
      - totals should remain percent
      - final grade should display points/possible points
  - go to SRGB with weighted groups - totals toggles should not appear unless unweighted
  - note: changing weights is broken currently, will fix in another ticket

Change-Id: I489d17c1dee699f9959f1b9036c4a05fa47aa91e
Reviewed-on: https://gerrit.instructure.com/30255
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Product-Review: Mike Nomitch <mnomitch@instructure.com>