translate grade report headers

refs CNVS-3134

test plan
 - grade report examples and report headers
   should be translated

Change-Id: Ib0ad3f67e990d70372882fa4315245c80500e73a
Reviewed-on: https://gerrit.instructure.com/34579
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>