Fix messaging for professional ed under auto-registration
Cleaning up a few quality violations
Updated outline template help text
Merge pull request #4856 from edx/markhoeber-documentation-outline-template-update

Updated outline template help text
Added note to doc team to update in both repos
Merge pull request #4895 from edx/ahodges/doc/preface

Added note to doc team to update in both repos
Merge pull request #4892 from edx/db/marcnu-quality

Cleaning up a few quality violations
Keeps in sync with edx-analytics-dashboard
Merge pull request #4897 from edx/ahodges/doc/twitter

Keeps in sync with edx-analytics-dashboard
Merge pull request #4886 from edx/will/ecom-122

Fix messaging for professional ed under auto-registration
Increase coverage of cohorts.py
Always return set in get_cohorted_commentables
assertEqual -> assertItemsEqual for sequences
Test cohort views, fix pagination in `users_in_cohort`
Test with non-staff users.
Fix `add_users_to_cohort` and `add_user_to_cohort`

When a user is being added to a cohort, verify that they are enrolled
in that cohort's course.  Also handle the case in which the requested
cohort is not found for the requested course.
Handle a nonexistent course in `add_cohort`.

Test more edge cases in cohorts.py
Address nits
Raise CourseEnrollment.DoesNotExist instead of User.DoesNotExist

(When the user to be added to a cohort is not enrolled in that
cohort's course)