problems with Field.setValue()

Fixed ArrayField.setValue() - it didn't set child elements of the ArrayField correctly.

Also made a change to Field.setValue().  I added the line

this.triggerUpdate();

So that when the values are set programatically, the dependencies are updated.

I've also added a new view, YAMLView.js, with an example (examples/components/layouts/yaml-layout.html) (the Edit YAML button is useful if you want to play with the setValue() behaviour).