Inter-app API cleanup for Grades

cms/djangoapps/contentstore/signals/handlers.py

cms/djangoapps/contentstore/tests/test_signals.py

common/djangoapps/student/helpers.py

lms/djangoapps/ccx/tests/test_views.py

lms/djangoapps/ccx/views.py

lms/djangoapps/certificates/api.py

...ps/certificates/management/commands/fix_ungraded_certs.py

lms/djangoapps/certificates/queue.py

lms/djangoapps/certificates/signals.py

lms/djangoapps/courseware/module_render.py

lms/djangoapps/courseware/tests/test_submitting_problems.py

lms/djangoapps/courseware/views/index.py

lms/djangoapps/courseware/views/views.py

lms/djangoapps/gating/signals.py

lms/djangoapps/gating/tests/test_integration.py

lms/djangoapps/grades/api.py

lms/djangoapps/grades/apps.py

lms/djangoapps/grades/config/waffle.py

lms/djangoapps/grades/constants.py

lms/djangoapps/grades/context.py