Nginx sample file and config files refactor

- Add a new configuration path inside install/config.
- Add htaccess.dist and nginx.dist inside the config path.
- Replaced old htaccess_dist mentions by the new one.

Refs: #5929
`/srv/example.org` would be better. Then use `example.org` in place of any `elgg`, `my-elggsite.dev`, and `elggsite` so that people can `sed` their way out of wasting time changing the paths. `/srv` is the FSH standard for server-specific data. `example.org` is RFC documentation-friendly, and enables automated customization without interfering with instances where the word `elgg` is actually required.