Request feeds for empty profiles from go-ssb

[mplorentz]

[boreq]

This involves at least two separate units of work:

• adding a function to our bindings; the function will temporarily add the feed to the want list
• triggering that function when viewing profiles, it should be enough to simply always trigger it when user navigates to the profile screen

[boreq]

@mplorentz It should be enough to call ssbFeedReplicate by calling GoBotInternal.replicate. We already do this for pubs and our own identity after logging the user in.

[rabble]

Go part is mostly done, needs to be coordinated with @boreq and @mplorentz for the swift side things to be done

[martindsq]

related to pull to refresh #792