Modified the database settings with ENVIRONMENT VARIABLE

The database settings in settings.py is now using dj_database_url to parse environment variable DATABASE_URL to get the parameter
DATABASE_URL has to be defined in the .bashrc as so :

export DATABASE_URL=postgres://ltbesh:pass@localhost:5432/ltbesh (for me)

and generally :
export DATABASE_URL=postgres://username:userpassword@localhost:5432/databasename