[REFACT] Move database url in settings to share it

gargantext/util/db.py

@@ -10,10 +10,7 @@ from sqlalchemy import delete
 
 def get_engine():
     from sqlalchemy import create_engine
-    url = 'postgresql+psycopg2://{USER}:{PASSWORD}@{HOST}:{PORT}/{NAME}'.format(
-        **settings.DATABASES['default']
-    )
-    return create_engine( url
+    return create_engine( settings.DATABASES['default']['URL']
                         , use_native_hstore = True
                         , json_serializer = json_dumps
                         , pool_size=20, max_overflow=0