Dockerizing the app: Fixing the removed couchdb auth, which causes "unauthorized" errors.

The authentication config was removed and the app crashes on Docker image with the
following error message:

{"unauthorized","reason":"You are not a server admin.}

The config settings for "auth" was removed a couple of commits ago. Addding it back and
reading using its default value along with the environment variables if available.

*	modified:   settings.js
- Adding the config property "auth" back with the default couchdb usr/pwd credentials.
- If the env vars from couchdb are defined, then use them instead.