Fix bug in FindDomainFilter where using some domains were not found

The ordering in `FindDomainsFilter._look_for_domains` was a bit off. The search for a something starting with `http|ftp` would happen, fail, and game over for finding a domain.

Instead, try to find a special key indicating this is a domain, if that fails, then look for  `http|ftp`.

Added tests to keep this working.