This commit adds a Docker Compose file which will run the application
using docker. The application is fronted by Traefik, and runs using
PHP-fpm. nginx is used to accept queries from Traefik and relay them to
the PHP-fpm containers (Traefik doesn't support FastCGI directly).
Sessions are shared between the various PHP containers using memcached.
Part of this work is based on [this repo](https://github.com/wandersonwhcr/docker-nginx-php-fpm)
