jsonalchemy: update readers and SmartJson

* Update all parsers to work with the new structutre of the field and
  model definitions, meaning using the extensions properly.

* When translating a new blob there is no need any more to go through
  the `readers` registry, instead call `Reader.translate`. See the
  method docs for more info.

* Update SmartJson to work also with new extensions and decorators
  structure.

* Update JSON for marc producer to adapt it to the new extension
  behavior.

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
records: update to new JSONAlchemy

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