* Don't create a `ContainerView` if there is only one connection.
* Don't create a virtual view if there are no connectors and the
block form of the plugin isn't used.
- allows passing of template data to the plugin-outlet to be rendered if no plugin is using that slot
- acts as a fallback when no plugin is found
- allows wrapping of existing features inside a plugin-outlet that then plugins can overwrite with their own behaviour
- backwards compatible
- uses invisible emberviews (as Ember.Component does)
- the template has full-access to the controller and view, should be totally transparent
