Better handling of proxies in translators

Re https://forums.zotero.org/discussion/42163/remove-proxy-information-from-url-field-on-import/
I'm not entirely sure that this is the best algorithm for the job. This works fine for translators that have strict URL requirements, because they will not match until the URL is deproxified. But other translators that have fairly loose requirements, or no requirements at all, will never get deproxified URLs. It might be better to reverse the order in which we check the URLs, starting with the "most deproxified" ones. This does hinge on our ability to detect potential TLDs correctly though, which could be a big issue if an actual subdomain (not proxied) contains something that resembles a TLD (that's quite reasonable I think).

I was thinking that we could take advantage of more specific translators (priority 100?) to detect proxies and then remember them in the current browser session. That would produce better results overall, but would cause somewhat inconsistent behavior early in the session until a site-specific translator kicks in.