Include IframeContentRenderer in editor-perseus.js exports
Include IframeContentRenderer in editor-perseus.js exports

Summary: Exposes IframeContentRenderer for use in the preview tab of the exercise editor.

Test Plan: - Verified in webapp that IframeContentRenderer is properly exported and is usable

Reviewers: kevinb

Reviewed By: kevinb

Subscribers: jared

Differential Revision: https://phabricator.khanacademy.org/D28900

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