Add an 'ssl-wrap-only' option

[Dariusz Suchojad]

The idea is to add an 'ssl-wrap-only' option to a URL's security configuration. Setting the option would mean that someone's interested in SSL-wrapping the traffic only, without any authentication scheme of whatsoever. In fact, setting ssl-wrap-only would mean any other options must not be set, that's to make sure someone doesn't mix things up inadvertently.

[Dariusz Suchojad (dsuch)]

'tis done and committed although in the end I've settled only on there being a requirement for 'ssl' to be True if 'ssl-wrap-only' is True.