R1:cd2e39025ea1

Add crumbs to Differential

Summary: Adds very basic crumbs to Differential, to prevent regression when we drop the application menu. I'll do a more proper pass at this but want to unblock landing the commit sequence for all this stuff.

Test Plan: Looked at detail view and list view, saw crumbs, clicked them.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T1960

Differential Revision: https://secure.phabricator.com/D4111