Address vulnerability in rack.
Read config values in code straight from ENV.
When config values are required in code, they are now always read straight from `ENV`. This removes use of YAML entirely. For local development an `.env` file is used (with the `dotenv` gem). This development dependency will be removed once migration to Cedar is complete and `foreman` can be used locally with a `Procfile`.
Merge pull request #25 from jdennes/do-not-use-yaml-for-local-config

Use .env rather than config.yaml for local config settings