Better vomnibar favicons

Fixes #1208; or, at least, it much approves on the situation.  And it does handle domains.

This fetches favicons from Google.  Helpfully, Google serves up a nice little "world" icon for anything it doesn't know what else to do with.  So we seem to get at least *an* icon for pretty much every site.

I don't think this is the final word on the matter.