ONMjs 0.0.24 bug fix in ONMjs.observers.NavigatorModelView...

... The Knockout.js view model triggered off assignment of the root navigator item model view (sub-objects created when the navigator is attached to a store). Previously, I've only initialized this class prior to instantiating the window manager so that the root assignment had always been made. And I have clearly never tested the detach functionality. The root navigator tree item is now held in a Knockout observerable so that a single instance of the class can be re-used through multiple attach/detach cycles w/different models and stores.