Add support for s2i to elections
    
    - Specify where the different configuration files can be found
    - Add an alembic_upgrade.sh script
    - Tweak gunicorn's configuration for logging
    - Adjust the requirements to include what is needed for s2i
    - Add a wsgi.py script to start the application
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>