If header values from a malicious client are passed to the backend
server unchecked and unchanged, the client may be able to subvert
security checks done by the backend server.
Move required files but 'nginx.tmpl' into a local 'app' folder and copy the
folder content into the image.
'nginx.tmpl' should be moved as well, but this is a breaking change for
configuration with a separate 'docker-gen' container.
