Fix issue #162 + improve nested validation highlighting

The ```fieldset.isValid``` property isn't necessarily initialized when the view looks for it to determine fieldset validity. I've introduced a validation method that counters this problem.
The validation method also ensures that any validation errors in nested Archetypes are highlighted on the parent/root Archetype.
Is there a better way to figure out if a nested property is an Archetype? I feel a little dirty checking the propertyEditorAlias like this...