fix 'hide students names' in GB when outcome gradebook is enabled

also - only init the gradebook slickgrid the first time the view is shown

fixes CNVS-12079

test plan:
- with and without outcome gradebook feature flag enabled
- 'hide/show student names' in the gradebook should work
- switch back and forth between outcome gradebook and gb2, it should remember
  your gb2 settings, like 'hide student names'

Change-Id: I0b8b0087bc1265a4af4a015cc10a3559b3af7685
Reviewed-on: https://gerrit.instructure.com/32737
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Braden Anderson <banderson@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>