Add fixtures for DB testing

[groovytron]

Fixtures can be easily defined and used for unit testing from what is said in Django testing documentation.

Travis has to be configured to use PostgreSQL following the documentation:

• Setting up PostgreSQL Databases in Travis
• Details about database credentials configuration
• Alternatively modify the settings.py file (seems nasty) to work with Travis

[groovytron]

Done here: 093b7c5fe5ad25534f4b3b05ebeec872a24595cf