PostgreSQL database for application deployment (production and test environments)

[stevelaskaridis]

Description

The application should be deployed on PostgreSQL rather than SQLite3 in production.
Testing should be also done with a PostgreSQL backend

Potential improvements

We could add, later on, support for different database backends.

[stevelaskaridis]

This issue would avoid having to deal with #56.

[NicolasLiampotis]

The idea is to use SQLite in development and PostgreSQL in staging/production environment.

So please rename issue to "PostgreSQL database for application deployment in staging/production" and modify description accordingly.