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Make kubectl explain print the Kind and APIVersion of the resource

**What this PR does / why we need it**:
Kubectl explain currently doesn't print out the Kind and APIversion of the resource being explained. When running `kubectl explain hpa.spec`, for example, there is no way of knowing whether you're looking at the `autoscaling/v1` or the `autoscaling/v2beta1` version. 
Also, `kubectl explain` is often used as a reference when writing YAML/JSON object manifests. It allows you to look up everything except the API version. Currently, you either need to know the API Version of a resource by heart or look it up in the online API docs. 
This PR fixes both problems by having `kubectl explain` print out the full Kind and APIVersion of the resource it is explaining.

Here are a few examples of the new output:
```
$ kubectl explain deploy
KIND:     Deployment
VERSION:  extensions/v1beta1

DESCRIPTION:
...


$ kubectl explain hpa.spec
KIND:     HorizontalPodAutoscaler
VERSION:  autoscaling/v1

RESOURCE: spec <Object>

DESCRIPTION:
...


$ kubectl explain hpa.spec.maxReplicas
KIND:     HorizontalPodAutoscaler
VERSION:  autoscaling/v1

FIELD:    maxReplicas <integer>

DESCRIPTION:
...


$ kubectl explain hpa.spec --recursive
KIND:     HorizontalPodAutoscaler
VERSION:  autoscaling/v1

RESOURCE: spec <Object>

DESCRIPTION:
     behaviour of autoscaler. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status.

     specification of a horizontal pod autoscaler.

FIELDS:
   maxReplicas	<integer>
   minReplicas	<integer>
   scaleTargetRef	<Object>
      apiVersion	<string>
      kind	<string>
      name	<string>
   targetCPUUtilizationPercentage	<integer>
```

**Release note**:

```release-note
Kubectl explain now prints out the Kind and API version of the resource being explained
```