Add revert_to_published method.

STUD-1860
Merge pull request #4344 from edx/christina/revert_to_published

Add revert_to_published method.
This emits enrollment mode changes events
Merge pull request #4309 from edx/nimisha/refactor_mixed_context_managers

Nimisha/refactor mixed context managers
Enables LMS to handle deprecated URLs

LMS-2651
Merge pull request #4285 from edx/jhelbert/enrollment-mode-change-events

Jhelbert/enrollment mode change events
Merge pull request #4353 from edx/flowerhack/lms-deprecated-urls

Enables LMS to handle deprecated URLs
LMS-2947 remove get_error_courses in Split.
LMS-2950 move delete_course to Mongo.