Basic ability to upload a CSV file.
Implement `add_users_to_cohorts` cohort API.
WIP: Implement bulk-cohorting as background task.

Conflicts:
	common/djangoapps/util/file.py
Get Jasmine tests running.
Add explicit upload button.
Add task unit test, remove CSV validation...

... to be implemented in django or backbone view for synchronous alert.
Add unit test for `unicode_csv_dictreader`.