Merge persons with the same name when merging works

[osma]

Currently when merging works we leave the persons (creator, contributor etc) intact. This often causes duplication of entities. For example, for the work W00009584100 (Ajan lyhyt historia), we get two contributors named "Sagan, Carl" and two named "Miller, Ron".

[osma]

This is difficult since we do the merging one slice at a time, and typically we don't know the author of the work we are merging with since it's likely asserted in a different slice.

[osma]

Options:

1. Do this kind of merging at the consolidation step, when we have all data available
2. Calculate merge keys also for persons and merge them the same way we merge works

[osma]

Here's a unit test for future use/adaptation.

@test "Merge works: merge authors of the same work with the same name" {
  make merged/kotona-merged.nt
  count="$(grep -c -F '<http://schema.org/author>' merged/kotona-merged.nt)"
  [ "$count" -eq 4 ]
}

[osma]

Also person subjects and contributors duplicated in W00591682300