Use proper file icons in lightbox

Summary: Ref T3612. Passes in file size and file icon for non-images.

Test Plan: Review a PDF and PSD in a lightbox.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T3612

Differential Revision: https://secure.phabricator.com/D16957