IPNS prefetching

I don't know how tricky this may be, but go-ipfs 0.4.18 has `--stream` flag for `ipfs name resolve` which makes it return names as they are discovered. It has some nice properties - names returned later are guaranteed to be 'better' (newer), last name returned before the stream is closed is always what would be returned by normal `ipfs name resolve`. This makes initial name discovery much, much faster, usually less than 1s from my testing.

When user goes to `/ipns/Qm..` path, companion could try to call `ipfs name resolve --stream` instead going directly to the gateway and prefetching/start displaying stuff in something like a sandboxed iframe (if something like this exists)