Develop authentication functionality that supports HTTP basic-auth

[rcrichton]

This functionality requires Koa middleware so be developed that ensures that application are authenticated using basic auth when they make a request of the OpenHIM. If they are not, then the request should be denied.

The user should be able to choose if they want to enable basic auth (see #12) or the PKI functionality or both.

More details about how this should work can be found here