Quick demo showing the use of dojo.Stateful APIs for derived values in a data model,
and binding between model and form dijits in the view.  The goal is to show a simple
means to conform to MVC patterns in UI design and also to emulate constraint-based
"derived" values in the data model using an image resize dialog.  

Try changing either the absolute or relative image sizes and observe the effects on
the derived values.  Changes can be made in either direction (absolute->relative or vice versa),
and also with the aspect ratio pegged or not.

While the demo does not actually implement a constraint-based dependency graph between
the values, the dojo.Stateful API along with simple checks to detect and break cycles are
sufficient to get pretty close...

The dojo.Stateful watch() fn is used both in the model for
derived values and to watch changes on the model to resync values in the view.
Future versions of the demo will extend the use of watch() to listen to property
changes in the view widgets, once dojo.Stateful is fully supported there, 
so we'll have a uniform model-model and model-view binding mechanism.  
Check out layer.js for details...