The Model/Thing Tree shouldn't show disclosure triangles if the Model has no Instances

(Bug, New , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
User Interface, UX
Summary: That is, in All Things (or the default Space Root page) we are showing the little triangle to display the Instances even if there aren't any. This wastes the user's time.
Observed by Ailis.