Pages MVC

So after a little basic work on vellum (and returning to it some months later), I've concluded that having a separate help pages app (or a pages app in general) doesn't really make any sense. The difficulty (keeping information updated across versions) is present in both paradigms and is something I'm working out the details of.

This PR represents a relatively minor code addition to core concerto and avoids the maintenance and overhead of the ~1300 line vellum plugin. It also acknowledges that we weren't going to ship core Concerto without help pages - making a plugin choice meaningless. I don't recall all the discussions around vellum (a recurring theme in design-decision land), so does anyone have a show-stopping objection to this?