Per review comments to
DM-3690, the configuration should move to YAML with the following goals
- Have a Configuration object that can be tested and passed around
- Redesign the configuration to allow for additional types of message handlers, such as twitter, hipchat/slack, etc.
- Move secret keys entirely into the configuration file
- Provide a configuration template
- Move any sort of hard-coded configuration to the expanded YAML file (e.g., Mandrill templates)