Make scope.Kind of pod/attach, pod/exec, pod/portforward, node/proxy,
service/proxy to their respective subresource Kind, instead of the
parent Kind. The kind is used by the admission webhook controller to
determine how to convert the object.
The registry abstraction is unnecessary and adds direct coupling to the
core types. By using a wrapper, we carry through the default
implementations of the non-mutating operations. The DeleteCollection
method is explicitly patched out since it cannot be correctly
implemented on the storage currently.
As a result, TableConvertor is now exposed.
A few other minor refactorings
* Corrected the case of some variables
* Used functions instead of methods for several helper methods
* Removed the legacy Deleter - service was the only remaining consumer
