Moved roles.py to common student

common/djangoapps/student/roles.py

lms/djangoapps/bulk_email/tasks.py

lms/djangoapps/courseware/access.py

lms/djangoapps/courseware/tests/factories.py

lms/djangoapps/courseware/tests/test_masquerade.py

lms/djangoapps/courseware/tests/test_roles.py

lms/djangoapps/dashboard/sysadmin.py

lms/djangoapps/dashboard/tests/test_sysadmin.py

lms/djangoapps/instructor/access.py

lms/djangoapps/instructor/tests/test_access.py

lms/djangoapps/instructor/tests/test_legacy_anon_csv.py

lms/djangoapps/instructor/tests/test_legacy_download_csv.py

lms/djangoapps/instructor/tests/test_legacy_forum_admin.py

lms/djangoapps/instructor/views/legacy.py

lms/djangoapps/open_ended_grading/tests.py