Add "Reveal Entire File" option to Diffusion

Summary: Clicks all the "Show All" links for you at the touch of a button.

Test Plan:

• Used "reveal entire file" on revealable files.
• Opened on already-visible files, got "entire file shown".
• Used other menu options.
• Used normal "show more" links.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, epriestley, btrahan

Maniphest Tasks: T497

Differential Revision: https://secure.phabricator.com/D1331