CloudFormation stack changeset property diffing

Little tricky to do right now, but property level diffs would be helpful to know why something is changing. I believe the CFN team is working on this as well, so it may not be worth hacking in for now.

It would also be nice to group the output by stage, it's not obvious from the verbose CFN ids. Also make sure I didn't forget to map any `AWS::*` types to a more user-friendly version.