Move the Docker files into dedicated folders for the according flavour

diff --git a/Dockerfile b/php-apache/Dockerfile
similarity index 100%
rename from Dockerfile
rename to php-apache/Dockerfile

diff --git a/docker-entrypoint.sh b/php-apache/docker-entrypoint.sh
similarity index 100%
rename from docker-entrypoint.sh
rename to php-apache/docker-entrypoint.sh