Determining differences between lists is hard

[jml]

#31 rightly made kubediff ignore list ordering, but it also made it harder than ever to understand what's wrong with a list.

e.g. consider a pod with one container. If the container definition varies, then we will now be told that the two lists of containers differ, that element 0 can't be found. We won't get any information about how the containers differ.

Some ways I can think to fix this:

• switch the structures to use pyrsistent so we can sort them and compare directly
• move this functionality to compare-revisions, where it would be super easy to add
• have dedicated types for each Kubernetes object (perhaps using an already-existing Python library?) and use those for equality comparison