R1:0b9101f3c5f0

Make lightbox close when the background is clicked

Summary: When you click the dark background, close the lightbox.

Test Plan: Clicked arrows, image, etc., to make sure it didn't close. Clicked background to close.

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3801