RFR: Support yaml metadata for actions and rules

* Add: Yaml support for actions and rules meta. Both yaml and yml extensions
are supported.
* Add: yaml, yml and json meta for sample action in fixtures for testing.
And for structured logging purposes, we should probably move towards using `extra` argument:

1. https://docs.python.org/2/library/logging.html#logging.Logger.debug
2. https://github.com/Kami/python-extra-log-formatters/blob/master/log_formatters/formatters.py#L23