Continuous deployment

[cbenz]

In short: make the web API (http://api.openfisca.fr/ reference instance) follow pip packages updates and always reflect the last OpenFisca-France tax and benefit system.

The problem: example: https://github.com/openfisca/openfisca-france/issues/449#issuecomment-196777735

Detailed tasks:

• [X] Install OpenFisca packages via pip (and not git) on the server (and add Python virtualenvs)
• [X] No more rely on mod_wsgi but gunicorn, use nginx instead of apache2/haproxy (because with mod_wsgi we can restart all the applications or nothing)
• [x] Watch PyPI OpenFisca packages updates
• [x] Auto-update when new version available for OpenFisca-France
• [x] Auto-update when new version available for Core and Web-API

[cbenz]

See https://github.com/openfisca/openfisca-ops