* Add COURSE_ENROLLMENT_CHANGED: sent after the enrollment update
* Add COURSE_UNENROLLMENT_COMPLETED: sent after the user's unenrollment
* Add CERTIFICATE_CREATED after the user's certificate generation has
been completed
* Add CERTIFICATE_CHANGED: after the certification update has been
completed
* Add CERTIFICATE_REVOKED: after the certificate revocation has been
completed
* Add COHORT_MEMBERSHIP_CHANGED: when a cohort membership update ends
* Add STUDENT_REGISTRATION_COMPLETED event after the user's registration
* Add SESSION_LOGIN_COMPLETED event after the user's login session
* Add COURSE_ENROLLMENT_CREATED event after the user's enrollment creation
* Generate common/djangoapps import shims for LMS
* Generate common/djangoapps import shims for Studio
* Stop appending project root to sys.path
* Stop appending common/djangoapps to sys.path
* Import from common.djangoapps.course_action_state instead of course_action_state
* Import from common.djangoapps.course_modes instead of course_modes
* Import from common.djangoapps.database_fixups instead of database_fixups
* Import from common.djangoapps.edxmako instead of edxmako
* Import from common.djangoapps.entitlements instead of entitlements
* Import from common.djangoapps.pipline_mako instead of pipeline_mako
* Import from common.djangoapps.static_replace instead of static_replace
* Import from common.djangoapps.student instead of student
* Import from common.djangoapps.terrain instead of terrain
* Import from common.djangoapps.third_party_auth instead of third_party_auth
* Import from common.djangoapps.track instead of track
* Import from common.djangoapps.util instead of util
* Import from common.djangoapps.xblock_django instead of xblock_django
* Add empty common/djangoapps/__init__.py to fix pytest collection
* Fix pylint formatting violations
* Exclude import_shims/ directory tree from linting
