records: better PID list

Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
uploader: files to link addition

* Adds new option for linking files with record via custom FFL MARC
  field.

* Adds `legacy` step to uploader insert worflow for filling-up "bibxxx"
  tables.  (addresses #1772)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
previewer: addition of support for Documents

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>