Show file comments on file lightboxes

Summary: Basic work in progress, but should show timeline comments for files when in lightbox mode. Looks reasonable.

Test Plan: click on images, see comments from timeline.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T3612

Differential Revision: https://secure.phabricator.com/D16896