Snapshot of work on navigator. This commit features creation of SCDL catalogue JSON via the entirely new navigator approach. Note that the navigator effectively functions as a graph builder using the objectDescriptor attributes of each menu item's layout declaration to determine what type of model view object to encapsulate, and where to register it. In the case of so-called "user" origin entities, the navigator instantiates "archetype" objects but does not automatically register them with the parent menu item host.