Add RestartPolicy to Pod and PodTemplate

This is the first PR to add RestartPolicy to Pod. Next PRs will hook policy with kubelets. 
So the argument is that append is wrong, and so everyone using Go should hide append inside a method that does the same thing that append does?  I guess from a readability and understandability perspective, can someone read and understand a standard language concept better than a wrapper around a standard language concept?  Would deploying wrappers around every append result in more bugs and confusion for code readers or less?