Introduce a new file to register filters

Add a Varnish container and enable cache invalidation

Switch to Symfony 3.3 stable

Fix Nginx's config

Revert #224; Upgrade to Docker Compose v3

This reverts commit e7e1ed6b.

Prepare for Symfony 3.3 and API Platform 2.1

Revert "Add PCRE dependency to the docker build for the php image."

Add PCRE dependency to the docker build for the php image.

Don't use ClassLoader component deprecated in Symfony 3.3

Fix IP whitelist in app_dev.php

No need for conditionals because we require PHP >= 7.0

Feature/docker update

Update config_prod.yml settings

Always use the dev env if the SYMFONY_ENV var isn't set