Automatic merge from submit-queue

Advanced audit logging API

This is an initial implementation of the API proposed in https://github.com/kubernetes/community/blob/master/contributors/design-proposals/auditing.md

This deviates from the exact API specified in the proposal in a number of ways. Here's a list of some of the changes I made, and why:

- General API conformance (`metav1.{Type,List}Meta`, +optional, etc.)
- Dropped fields that won't be part of the initial implementation (storage objects & filters), to be added later
- {Request,Response}Body -> {Request,Response}Object - This is actually what the proposal originally had, and will be much better for adding Filters later, and provides a less protocol-dependent API. Note that there is currently no way to include Response body for non-resource requests.
- Drop HttpMethod - redundant with verb
- Response{StatusCode,ErrorMessage} collapsed into `ResponseStatus *metav1.Status` - This is the standard response type for resourec errors, but can hold genereric error responses too. Note that this is part of the `Metadata` Level.

/cc @kubernetes/sig-auth-api-reviews @kubernetes/api-reviewers