Update letsencrypt_pre_hook.sh to stop web server if any exist because standalone needs to use http port 80 in case the web server is installed later.

Update letsencrypt_pre_hook.sh to check for OS and other firewall or use iptables. Not fully tested.

Add new file "letsencrypt_pre_hook.sh" to support letsencrypt standalone during ISPConfig installation or update for non-webservers. Webservers shall always use webroot.