Allow to deploy sao on subpath

Following https://discuss.tryton.org/t/nginx-configuration-with-rewrite-dose-not-shown-database-list/2605/10

This setup can be done using and nginx server in front of the trytond server. Here is the configuration neeeded:

location /tryton/ {
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_pass http://localhost:8000/;
}
location / {
root /usr/share/nginx/html;
index index.html index.htm;
}

It should be possible to access tryton from http://localhost/tryton/