Initial checkin of the deferred instantiation feature for Gumbo.
ItemsComponent has a "creationPolicy" property that controls when the content items are created. Possible values are:
* "all" - content is created as soon as the ItemsComponent is created
* "auto" - content is created as soon as it is needed
* "none" - content is not automatically created. When this creationPolicy is set, you must call createDeferredContent().
The "contentCreationComplete" event is sent when the content has been created.
Added IDeferredContentOwner interface. ItemsComponent is the only Gumbo component that implements this interface.