Fix relative import of base settings

I just tried out your template project for one of my own and got an import error for the ``local.py``:

```
ImportError: Could not import settings 'synpho.settings.local' (Is it on sys.path?): No module named base
```

Looking at the files importing ``base`` it seems like the imports are supposed to be relative but are defined as absolute. Your code snippet in the book confirms that that's the intended way. I fixed it in the three settings files. I am a bit confused though since it seems that others have used the project successfully. So if I am missing something really obvious, just ignore this :smile:

Oh, and thanks for a great book. It's a great and educating read :thumbsup: