Move raw file download icon to file box in Diffusion

Summary: For images and text, show the "Raw" buttons on the file's ObjectBox

Test Plan: View an image and a text file in Diffusion, click on the download link in each.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4467

Differential Revision: https://secure.phabricator.com/D8302