Allows support staff or global staff to view a list of a learner's
enrollments, and change enrollment modes. We generate a
ManualEnrollmentAudit record for these enrollment changes in order to
track updates. Additionally, enrollment changes are handled through
the enrollment API, which handles bookkeeping such as granting refunds
where appropriate.
ECOM-2825
* Add new role for support staff.
* Move dashboard/support functionality into a new Django app called "support".
* Add support view for searching and regenerating certificates.
* Refactor certificates views into separate files.
