Support solution in the shape of html texts instead of videos
Support text solutions in teacheradmin
Some usability improvements in teacheradmin questions interface
Don't return the solution text for exams or homework before the deadline
Add a new field feedback to options model
Ignore warnings to avoid cluttering the logs
Cosmetic change
Add an email subject prefix
Validate the option's types when checking if they are correct
Add commands to export and import teachers from a course
Validate the answer type in the API too
Fix teacheradmin navigation urls
Merge branch 'master' into feature-solution-feedback

Conflicts:
	moocng/locale/es/LC_MESSAGES/django.mo
	moocng/locale/es/LC_MESSAGES/django.po
	moocng/static/js/teacheradmin/units-views.js
Resume migrations in one
Support feedback in question editor
Always show the link to the question editor in django admin

Since we have now the "no-image" image and the blank canvas.
Paint feedback button next to wrong options
Improve feedback button style
Improve question editor styles
Stats' navigation dropdowns are disabled when empty