SOL-495 Cohort-Aware content search

cms/djangoapps/contentstore/course_group_config.py

cms/djangoapps/contentstore/courseware_index.py

cms/djangoapps/contentstore/tests/test_courseware_index.py

cms/djangoapps/contentstore/views/course.py

...pps/contentstore/views/tests/test_group_configurations.py

common/test/acceptance/pages/lms/courseware_search.py

...ceptance/tests/lms/test_lms_cohorted_courseware_search.py

lms/envs/common.py

lms/lib/courseware_search/lms_filter_generator.py

lms/lib/courseware_search/lms_search_initializer.py

lms/lib/courseware_search/test/test_lms_filter_generator.py

...lib/courseware_search/test/test_lms_search_initializer.py

requirements/edx/github.txt