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

The big per project use case is to allow us to define the name suitable for our use (I consider oracle/mysql canonical, so I call it mysql, but you like percona/mysql which you call mysql as well).  There's a certain amount of value in being able to set both global and project scoped names - for instance, I want to track the global mysql but I want to override the metadata with a minor tweak.  Not a blocking case, but two teams in the same project might use different versions of tomcat or mysql or redis.