[WIP] Add support for Config{} to kubecfg

This PR will allow users to use simple JSON file with arrays of Kubernetes objects (services, pods, replicationControllers) as a parameter for `kubecfg -c config.json apply` command.

The [example JSON](https://github.com/mfojtik/kubernetes/blob/config/examples/config/guestbook.json) file in `examples/config/guestbook.json` contains all objects required for deploying the [guestbook example](https://github.com/GoogleCloudPlatform/kubernetes/tree/master/examples/guestbook).
We have an api.XList object already, for all of these. Might make sense to use it.