Mabmapper-port: Extended signature and signature_search for journals

https://github.com/ubpb/mabmapper/commit/c6a314c2e5c065f99b40d2a9d45a266c0d4b327a
  but access to doc.fields('LOC').subfields('b') is changed,
  now validating uniqueness of subfield 'b' over all 'LOC' fields
Version bump