PVC: Return empty Archetype instead of null when empty/errors
Make Archetype Model enumerable to simplify usage, make Fieldsets internal
Add "Hide Label" option for full-width Archetypes
Allow single rows to be collapsed

Previously, you couldn't collapse a single row by itself, it was always expanded.  Now you can collapse it, but it's still expanded on the initial page load.
Added methods `HasProperty` and `HasValue`

Added methods to the `Fieldset` object for checking if a property exists and/or if it has a value.
Merge pull request #86 from leekelleher/feature/fieldset-methods-hasvalue

Added methods `HasProperty` and `HasValue`
Merge pull request #85 from imulus/feature/collapse-single

Allow single rows to be collapsed
Merge pull request #84 from imulus/feature/hide-label

Add "Hide Label" option for full-width Archetypes
Merge pull request #81 from imulus/tweak-pvc

Simplify PropertyValueConverter
Merge branch 'develop'