Move templates to S3, with option to have locally

[lox]

I'd like to publish the Cloudformation templates to s3 and reference them from the CLI rather baking them into the binary.

This sets us up to be able to have nested templates, as well as fairly easily supporting user-provided templates or copying them to your own template.

[pda]

Worth noting nested CloudFormation templates/stacks don't seem to play well (or at all?) with Change Sets: https://forums.aws.amazon.com/thread.jspa?threadID=228489 Even aside from that, I am personally not a fan of nested templates. I think CloudFormation does need some modularity mechanism, but I don't think the existing nested templates is the right way.

Putting them on S3 instead of in the ecsy binary does seem like a good idea, though, as long as they're well versioned.