Project settings organization more clear.

Hello Roland,

First, thank you for the nice djangorecipe. I find it very useful and it's great to know it stills in continuous development :)

I know it's just a personal matter, but usually I find more tidy in a Django project to have a `settings` directory containing the settings files, since almost all developers use to have different settings for different environments.

For this, I made a little modification to the djangorecipe. Basically, instead of creating the three settings files `settings.py`, `development.py` and `production.py`, now creates a `settings` directory which contains those files. I renamed `settings.py` to `base.py` to be more clear.

I also reviewed the unit tests related to this changes, adapting them to the new behavior.

I made this pull request to share the changes with you, just for your interest. So, feel free to include it in the official djangorecipe if you like it or to refuse if you want to keep the current schema.

Anyway, thanks!