Let LWP::UserAgent handle https-proxy commands

This also makes it possible to do proper SSL certifcate verification. So the new option WebUserAgent::DisableSSLVerification is removed again.

For accessing HTTPS resources via a proxy server, HTTP CONNECT is used only LWP did not support this properly. See https://en.wikipedia.org/wiki/HTTP_tunnel#HTTP_CONNECT_tunneling This is why we had the workaround of using Net::SSL in place.

Only, since LWP 6.06 LWP now supports this properly. See https://en.wikipedia.org/wiki/HTTP_tunnel#HTTP_CONNECT_tunneling this means the whole Net::SSL workaround, and the cruft around this, can be removed!