PageRoutingHelper: Can this be lazy loaded and accessed via ICofoundryHelper

[HeyJoel]

We need to check the design of IPageRoutableViewModel and PageRoutingHelper. This is instantiated in the page route with the full directory of pages, but I think lazy loading this on-demand would be a better strategy.

This could perhaps be incorporated in the ICofoundryHelper in a similar was to the user state.

Issue #266 includes some background info on why this data is useful. It's also useful for building sitemaps and breadcrumbs.