Adding back the Graded Group widget.
Adding back the Graded Group widget.

Summary: Asana: https://app.asana.com/0/265849773833386/389591139887668

Test Plan: - Edit any article and see that "Graded group" appears in the widget dropdown

Reviewers: scottgrant

Reviewed By: scottgrant

Subscribers: jared

Differential Revision: https://phabricator.khanacademy.org/D38039

ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus