R1:26c0db8dd797

Allow navigation breadcrumbs to be marked as "always visible" so they show up on phones

Summary:
See PHI624. Some of the mobile navigation and breadcrumbs in support pacts aren't as good as they could be.

In particular, we generally collapse crumbs on mobile to just the first and last crumbs. The first crumb is the application; the last is the current page.

On `/PHIxxx` pages, the first crumb isn't very useful since the Support landing page is two levels up: you usually want to go back to the pact, not…