Support tool for changing enrollments.

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

common/djangoapps/student/models.py

@@ -1489,7 +1489,7 @@ class ManualEnrollmentAudit(models.Model):
         """
         saves the student manual enrollment information
         """
-        cls.objects.create(
+        return cls.objects.create(
             enrolled_by=user,
             enrolled_email=email,
             state_transition=state_transition,