Add a masked image to Pholio Inline Comment Dialog

Summary: n/a

Test Plan:
Tested both ajax and regular pages, test various comments, images.

{F168592}

{F168593}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9630