Accounts roles allowed: 'admin', 'app', 'user'.
Disable cache-control on 'accounts' endpoint.
Token Based Authentication.

For user authentication we're now using Token Based Authentication.
Since the API is going to be running on SSL we're fine with this
variation of Basic Authentication.

For details on Eve authentication handling see:
http://python-eve.org/authentication.html
User and pw for running on a local mongo instance.

Sensible settings like these are retrieved from environment variables on
the hosting einvironment (Heroku). If these envs are not available then
we're running on a local dev instance, therefore we set some defaults.