Move Diffusion Browse to a single column layout

Summary: The main change here is moving (compare, search, history) into buttons in the header bar on all browse views. This allows Directory Browsing to be full width, since there is no other curtain information. File, Image, LFS, Binary all stay in TwoColumn layouts with the same buttons in the header.

Test Plan: Test viewing a directory, file, image, binary file, readme, and fake a gitlfs.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D17766