Proposal: Initial images proposal

This is a proposal to add a higher level image component that can keep track of Docker image repositories, images, and image metadata.

This is not about reinventing how Docker handles images or an attempt to make Kubernetes also a Docker registry; instead, we're hoping to facilitate concepts such as:

- a virtual unified view of image repositories potentially spanning multiple registries
- reacting to image changes to perform a variety of actions, such as downstream builds or new deployments
- allowing users to override default image metadata consistently when an image repository changes
- dealing with Docker image metadata in a time series, for the purposes of making images easily consumable by other components of a deployment system

If you do the proxy approach, could you stuff extra metadata about images into the "docker inspect" metadata.   Ideally, a PR could be sent to Docker to add official definitions for at least the non-k8s specific properties.

Presumably container orchestration systems other than k8s would benefit from some of these types of metadata and a standard at the docker level would mean more package maintainers would fill in properties if they can.