Remove django-discover-runner app.

Because it has been added to Django 1.6 as the default test runner.
Merge pull request #108 from mozillazg/remove_django-discover-runner

Remove django-discover-runner app
Update CONTRIBUTORS.txt
refractor(settings): break up the settings into one module per configuration

- moves urls.py to project_root
- moves wsgi.py to project_root
- 'config.settings' is replaced by 'config', selectively applicable
  configs are imported in '__init__.py'

fixes: #47