Fix cohorting views

Use old deprecated form for instructor api calls, and in staff debug info

Sarina/course modes display

Dhm/bug ok serial numbers

Added asserts to ensure course_ids are course key objects.

Fix management commands

Fix certificate requests

Clean up logging in import_export.py

Make mongoengine field for UsageKeys expect a Location

Migration for role_coursenum deprecated roles

Call other CourseModeView methods using serialized course_id

Remove dead code

Don't use Empty directly, let the manager handle it

Make the arguments to translate_location_to_course_locator more specific

Fix ConditionalTest test system

Fix PsychometricData query

Allow cross course references in the LMS

Handle malformed keys in MixedModuleStore configuration

Fix student progress @sarina bug