Fix mixed content issue

A lot of the links to external resources are hardcoded with https:// and cause mixed content issues when using https. Additionally we are using HTTP/2 which is even tighter on security so insecure resources are simply not loaded at all. One example is the gmap shortcode that does not work at all under https.

Please at least change HTTP:// to only // so the browser may pick protocol.

https://www.ads-software.com/plugins/shortcodes-ultimate/