First cut at a photo migrator old-embed -> hecuba.

Still has some issues, but the bones are there.

It seems that some of the paths in the existing data are invalid.

e.g.

select id, photos from entities where
id='adce5e2650f7532e26b969a3f8743fab3df7cadd';

the path to the photo doesn't exist.
photo migrator works, and is a bit more forgiving.
Merge pull request #143 from MastodonC/feature/old-embed-photo-migration

First cut at a photo migrator old-embed -> hecuba.