Modernize Diffusion Create with sidenav, curtain

Summary: This moves the navigation to a standard sidebar, and moves all actions to the curtain. Also pulled out info view when available for cleaner UI.

Test Plan:
Create a git, svn, hg test repository and verify each page in the sidebar renders as expected.

{F4973792}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18003