We can determine diaspora_handle from a relation with people for the
shareables (posts, photos). So we don't need to store diaspora_handle in
the DB. Also remove tmp_old_id from photos which is not refenrenced anywhere.
These are some initial tests, more to come.
It tests some features of Request, StatusMessage, Comment, Like,
Participation, Retraction, SignedRetraction, RelayableRetraction entities
receive process.
