webif: Load external jquery files using // protocol (auto http or https).

When SSL and external jquery is used in webif the browser comlains about
usage of insecure elements in secure page. The browser is right to complain.

This fixes ticket #3712.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@9660 4b0bc96b-bc66-0410-9d44-ebda105a78c1