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

Improve Docker support on Windows

Use --classmap-authoritative for Composer install in prod mode

Upgrade PHP and APCu

Use recommended settings for performance in php.ini