kubectl delete command: adding  labelSelector

@lavalamp @smarterclayton basically I've rewritten the PR integrating your comments.

@smarterclayton: I didn't fix shortcut expansion since I have hard time to understand where the shortcut should come from. Maybe we may discuss about it. 
I was trying to avoid baking these into ResourceInfo (so that ResourceInfo can be used by a comment).  Let me send you a pull to your branch that suggests what I was talking about.