Update grades to use Block Structures

common/lib/xmodule/xmodule/course_module.py

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

lms/djangoapps/certificates/queue.py

lms/djangoapps/courseware/grades.py

lms/djangoapps/courseware/model_data.py

lms/djangoapps/courseware/tests/test_grades.py

lms/djangoapps/courseware/tests/test_submitting_problems.py

lms/djangoapps/courseware/tests/test_video_mongo.py

lms/djangoapps/courseware/views/views.py

lms/djangoapps/instructor/features/data_download.py

lms/djangoapps/instructor/offline_gradecalc.py

lms/djangoapps/instructor/tests/test_offline_gradecalc.py

lms/djangoapps/instructor_analytics/basic.py

lms/djangoapps/instructor_task/tests/test_tasks_helper.py

openedx/core/lib/cache_utils.py