jsonalchemy: preserving original tags inside JSON
- When using creator rules that involves regex like 245.. the original marc tag is preserved inside the __meta_metadata__ key for posterior needs.
- Enhances json_for_marc producer to use the input tag if the producer is defined to do so (See json_for_marc documentation). (addresses #1722)
Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>