Adds visibility for grading_standard_id and grading_standard_enabled boolean to Course Settings API
Merge pull request #536 from redconfetti/CLC-4413-course-settings-grading-standard

Course Settings API - Grading Standard visibility

Change-Id: If96be8ffa03aefe3553eb5a67968f6f81a839090
Reviewed-on: https://gerrit.instructure.com/43493
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Reviewed-by: Cameron Matheson <cameron@instructure.com>