Align connector detectWeb rules with Firefox

Chrome connector seems to like this. I'm having a bit of a hard time finding test cases atm (some of the pages that were reported don't seem to have embedded iframes anymore), but reverting https://github.com/zotero/translators/commit/2ca80898871b5039cf25c330859ee195885e11bc and navigating to http://www.forbes.com/sites/peterlipson/2013/04/19/a-film-producer-a-cancer-doctor-and-their-critics/ doesn't work on the current connector, but does with this patch

I haven't tested Safari connector.