xchat: openssl fix

Primarily, a fix to shove xchat off of using the system OpenSSL. Otherwise, general modernisation and passing the new strict audit.

I’ve also allowed the applications/pixmaps folders to be installed again, since we allow plenty of that in the core, and they can actually be rather useful for x11 applications to keep. I had a good scout around the core for issues as to why they were removed, but there didn’t seem to be any.