Allow creating LE SSL certs during ISPConfig 3.1 stable install or update, webserver (webroot) or non-webserver (standalone). UFW will be installed if it is not found. All have been tested except for installing ufw on centos. Developers may want to further test this. Submitted for 3.1 stable as suggested by @tbrehm in the forum. Similar PR have been submitted to master 3.2 (to fix previous merger) as well.