Unit test for faulted earth

Implements the first unit tests for the Faulted Earth application.

To launch the test independently, activate your virtualenv and issue

```
python ./manage.py test observations/tests.py --noinput
```

from the django project directory.

To update an existing installation, mind the creation of a template_postgis template database as done in the installation script (line 374).


I have also rebuilt the initial migrations (I still think that we should disable them).