Fix typo
Added unique flag for slug fields in announcements and courses
Added missing migration file for courses model and removed debug line from youtube handler
Added badge selection to teacher admin panel
Added cleanframes management command. This command removes unused question images.
Added course field to contact form, added course to message body
Fixed missing tag in teacheradmin
Added "hidden" mode to courses. This will keep the course active but won't list it on the platform
Added hidden to allowed public modes
Added redirect of orphaned course url to courses list
Merge branch 'master' into mongo_refacts
Rename statistics migration