Add support for multiple input artifacts to the CloudFormation action

[john-shaskin]

1. Added in unit tests to verify base functionality of the CloudFormationAction class
2. Updated the interface for CloudFormationAction to take an array of input artifact names, instead of a single one. This impacted the configuration for the path to the input CF template and the configuration files. So consumers are now required to pass the whole ArtifactName::path/template.json string instead of just path/template.json.
3. As a minor update, I renamed the tropo.py and associated test file and consumers to reflect that the class is TemplateQuery.