Ensure that kubectl get works with downstream resources

Commit a198a62 introduced a dependency linking the Kube API versions to the implementation
of watching resources used in kubectl.  This removes that dependency and allows conversion
to be handled by the ObjectConvertor defined in the kubectl factory.

@lavalamp review please
A function in the interface is better than a public variable here, IMO-- as written, users have to write a type switch and know about every possible printer type to get at this. Can probably just make it private for now, though.