Add nginx support and set defaults

As part of https://git.coop/webarch/chat I had to modify a bit to work for nginx, but not much.

I found the default installation of nginx is actually ok for serving the .well-known files (although we may want to extract a general nginx reusable role with a better default, e.g. https://git.coop/webarch/chat/blob/master/roles/nginx/files/default).

Also added some defaults, which means I didn't need any vars in my playbook :) https://git.coop/webarch/chat/blob/master/setup.yml