[#3] Fix HTTP 403 (Forbidden) errors

Associated issue: #3 (closed).

Currently, the Apache server attempts to use port 9000 on the php container for handling PHP files and loads all other files from /var/www/html - however, /var/www/html does not exist in the Apache container. This results in the error: Forbidden - You don't have permission to access this resource.

The web files from the php container should be shared with the apache container, mounted at /var/www/html. A volume called www-data will now be mounted on the php container and then mounted on the apache container at /var/www/html. This allows both the containers to access these files.

Closes #3 (closed).