Is a Model
All Things can be used as Models if you would like -- in Querki, unlike most programming
languages, the difference between a Model and an Instance is pretty small. But this flag indicates
that this Thing should normally be considered a Model. If you set it, then this Model will be
offered as a possibility when you go to create a Thing, it will be displayed a bit differently in
the Space's list of its Things, and in general will be handled a little differently.
