Add a list view to the declarative UI with items built from components

[cmeyer]

• Add a create/destroy protocol for grid flow item factories.
• Add a declarative item factory for constructing list item components.
• Add a declarative list view element with templated items.
• Wire the list view current index, selection, and item events.
• Expose item selection state to list view item components.
• Add a list view demo page to the ui demo application.
• Focus items inserted into a focused grid flow canvas item.
• Reimplement the list box on the list view with a text item template.

From demo:

Expected to be used for a general list-detail browser.