This method should probably be enhanced to support different widget libraries and return a list of objects instead of the first result

* different widget libraries is needed for widgets like `Template`, `RadioButton` and `CheckBox` that are in both `aria` and `html` library
* returning a list of widgets would allow to select more specifically the widget needed. Say for instance that you want the second checkbox in the page, or the one that has a certain value or is bound to a given object.

The signature could be

`getBehaviorByType : function(type, ctxt, match)`

where
* `type` is either a `$class` or a `$classpath`
* `match` is a match function that gets called with the index in the iteration and the widget. This method can be defined by the user and should return true when some conditions are met.

What do you think?