Revert "Write unit tests for weather.config"

This reverts commit afe238274921c835d309d377d639e211738a2573.

Accidentally included unintended modifications to settings.py
Write unit tests for config.url_helper

Create empty models.py so that 'config' can be declared as a formal Django app
and be tested alongside of 'weatherapp' without needing additional
configuration. Unit tests for the 'url_helper' module check return values as
well as required args.