It doesn't make sense to print out unavailable students
since it will go negative as students unenroll

This will allow you to force the certificate generation
for when certificate requests are lost and stuck in
'generating', this happens when we have xqueue issues.

graded

* List of courses that have ended is now a generator
* Using db-aggregation to speed up query for tallies

* Removing the command to find unicode names since it was only used for
  testing
* ungenerated_certs will now by default run through all courses that
  have ended.  a course option can be used to run on one course
* gen_cert_report added which will summarize certificate states
  for all courses that have ended

enrolled_students query

Updated for testing (for now)
This will eventually be run periodically and/or server
as a way to generate certificate requests from the commandline

Conflicts:

	lms/djangoapps/certificates/models.py