Implements #5290 in stable branch: Nginx - Allow certbot acme challenge on auth_basic protected websites

Add description text for logging options.

Fixed: #4307 The new LE ssl cert paths introduced in ISPConfig 3.1.1 where not set in the nginx_vhost.conf.master

The cipher suites are only set now for ISPConfig's own vhost, the intermediate security profile from Mozilla is used here.

- backported patches

see:
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_454

- http://en.wikipedia.org/wiki/SPDY

- nginx: merge function: default action is now to replace older locations in the nginx vhost configuration; a merge  instead of a replacement can be achieved by putting the string "##merge##" (without quotes) at the end of the most recent location line (e.g. "location ~ \.php$ { ##merge##").