The notifications center's delivery API will listen to /delivery.

We initialize a Flask application with a /delivery/status 200 alive
reply to let monitoring tool and production environment tests check
if the application is up.

This commit has been done in the Francfort-Bruxelles ICE, with wifi aboard.

1. Run it through ./app.py
2. Browse /, get a 4O4
3. Browse /delivery/status, get a 200 ALIVE