Audit log

Right now `up deploys` only shows the deployment history, which is fine, but it would be nice to replace that with something like `up history` (name suggestions?) to display all relevant events such as applying stack changes and rollbacks using AWS CloudTrail.

It may be tricky to filter out events that are only applicable to the app, needs a bit of investigation. Otherwise rollbacks don't really have any "trail" I can use to display in `up deploys` etc, aside from showing the current version.