So there is a "mode" field - I'm not sure what it means, also I'm not clear on the difference between CertificateItem and PaidCourseRegistration.  @dianakhuang should probably weigh in here, since she likely has all of the domain knowledge!

DB vs. cookie is largely an architectural/cultural decision... not sure what we've done in the past, but we should probably be consistent with the patterns people have used before.