BasicAuthenticationClient now takes python dictionary, instead of Config...

... object. More consistent with java version of auth client, and this also more easily enables users to work with other types of authentication clients (doesn't require them to create a new Config class for a different type of AuthenticationClient. Config.py was basically a restricted dictionary.
A user would also need to implement this function if they want to read credentials from a file. 

Perhaps we should have another method ``auth_client.configure_from_file(filename)`` that takes in a file and does this.