Proposed ContainerStatus for each individual Container in a Pod.

@smarterclayton @thockin @bgrant0607 @brendandburns 

I started to work on termination reasons #137. Before I go crazy, I would like to propose a new struct to our API, which hold all information of a container related to a BoundPod. This PR does nothing with many TODOs
for further discussion. 

@smarterclayton I mentioned this to you in one of your v1beta3 API proposal (#1225). But I think we could have this in now without breaking any clients. Without my PR #1199 and #1262 in, we don't have correct PodInfo anyway. 
Yeah, I'd suggest making a ContainerStatus type.

Also consider just naming the field "Status" since you're already in a ContainerStatus struct.