expose more course settings via API

fixes CNVS-17625

test plan:
 * Exercise the Get course settings / Update course settings
   APIs and ensure the new settings work (API settings persist
   and are reflected in the Course Settings page)
   - allow_student_organized_groups
   - hide_final_grades
   - hide_distribution_graphs
   - lock_all_announcements

Change-Id: I422bb507388032594cbe592543699b64f143cf78
Reviewed-on: https://gerrit.instructure.com/46197
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Product-Review: Dan Minkevitch <dan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>