Add pattern search to diffusion home

Summary: Moves the method up to DiffusionController, so it can be more universally used. Also now center aligns tabs on mobile. Still todo, get search nicely toggled on mobile

Test Plan: Test mobile, desktop. Test search from home, from browse, and browsing a specific path.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18432