The previous logic was a convoluted way of doing the same thing, and
has already led to one bug. Instead of hoping that the bugs are ironed
out now and that future devs maintain this logic properly, let's just
set a real cutoff date.
Two new certificate statuses are introduced, 'audit_passing' and
'audit_notpassing'. These signal that the GeneratedCertificate is not
to be displayed as a cert to the user, and that they either passed or
did not. This allows us to retain existing grading logic, as well as
maintaining correctness in analytics and reporting.
Ineligible certificates are hidden by using the
`eligible_certificates` manager on GeneratedCertificate. Some places
in the coe (largely reporting, analytics, and management commands) use
the default `objects` manager, since they need access to all
certificates.
ECOM-3040
ECOM-3515
Add the ability to generate "example" certificates to
test that certificate generation is working correctly for a course.
Add the ability to enable/disable self-generated certificates
on a per-course basis.
