Explicit preference to ignore URL fields

[1ec5]

AVIM ignores the URL bar and any <input type="url"> fields when urlbar is in the blacklist. But the blacklist is intended for matching element IDs, not element types, and it’s a very advanced preference. Instead, there should be a dedicated preference for ignoring URL fields, like the password preference. When migrating users to the new preference format, urlbar should be removed from the blacklist and the new preference should be set.