bibindex: move new files to legacy and fix imports

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
search: update fixtures and models.

* Updates `Tag` fixtures and models accordingly to the new indexer
  capabilities to index non-marc records.

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>