Separate URL confs by environment

Create environment-specific URL conf handling. Put the handling of Django static file serving for development in urls/dev.py rather than the root urls.py and relying on settings.DEBUG.

Updated project folder structure:

```
project_name / 
    + urls /
        - __init__.py
        - base.py
        - dev.py
```

`dev.py` settings file has ROOT_URLCONF set to dev url conf.