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`.

Update input file format, remove validation from async code
First bok choy test

Support either username or email (instructor_user is failing).

Celery tasks now work in bok choy.
Update output format

Fix task progress reporting

Fix bug; support either username or email
More bok choy tests and introduction of validator.
Move `add_users_to_cohorts` view to instructor.views.api

Change validation logic.
Fix validator and cleanup tests.
Use `with` statement to open input csv in task helper

Verify CSV output.

Test input csv with too few columns

Use unicodecsv, fix csv input with too few columns
pep8/pylint cleanup