[Smtk-developers] Model association changes

[David Thompson]

> I've pushed a first batch of changes to treat associations as special ModelEntity{ItemDefinition,Item} instances. ...

The second (and hopefully final) batch of changes has been pushed.

> ... This was done so that attributes can specify the number of associated entities as well as their type. For example, it is possible for attributes representing SMTK model operators to indicate that only a single model may serve as the workpiece (say, for a subtraction operator). ...

This should also make it much simpler to expose associations in the GUI since now they can be treated as just another item belonging to the attribute.

	David