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

Fix a typo on doc URL and stable version

Remove pre-existing PID file before starting apache