Make drupal.conf extendable

[iBobik]

In #15 I proposed to add support for specific Drupal module, but @zaporylie do not want to have this kind of config in common image and proposed to: "make nginx *.conf structure more flexible and pluggable so you could easily add s3fs.conf rather than overriding entire drupal.conf configuration"

So how about to move drupal.conf out of /etc/nginx/conf.d and add include /etc/nginx/conf.d/*.conf; into server block, so users can extend image just by Dockerfile like this:

FROM drupaldocker/nginx
COPY project.conf /etc/nginx/conf.d/

And simple project.conf with just a few lines what will be inserted inside server block (so they can reuse macros from drupal.conf like @rewrite)?