Make FreebaseObject public again

I made FreebaseObject internal in the previous updates. This is not correct, or at least has unintended side effects where "MainImage" is no longer public to reflection and thus visualization code that depends on this breaks (though this is not related tor recently reported errors). We may revisit this again but for now we can just revert this bit. Also make the "Id" property public.

Also some false entries were showing up in the domain category list due to recent additions of /user entries in the domains in the domain category list.