Changed the path in set-image-blocker's redirection default to

Changed the path in set-image-blocker's redirection default to
"send-banner?type=pattern" instead of "show-banner?type=pattern"
which isn't caught by Privoxy. Fixes BR 1573468.

Changed hide-user-agent's default value to "Privoxy VERSION".

Changed hide-referrer's default fake value to "http://www.privoxy.org/".
A static referrer is obviously fake anyway, so we might as well
advertise ourselves.