BibIndex: centralisation of synonym treatment
BibIndex: centralisation of synonym treatment

* Removes CFG_BIBINDEX_SYNONYM_KBRS variable and moves the per-index
  synonym definitions to the database.  Adapts BibIndex Admin
  interface accordingly.  (addresses #852)

Co-authored-by: Grzegorz Szpura <900c4f131187ed2a7cfcf1f0200fa0b9c64b7780@cern.ch>
Signed-off-by: Grzegorz Szpura <900c4f131187ed2a7cfcf1f0200fa0b9c64b7780@cern.ch>
Tested-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

tiborsimko/invenio-search,tiborsimko/invenio-records,inveniosoftware/invenio-records,inveniosoftware/invenio-search,tiborsimko/invenio-records,tiborsimko/invenio-search,inveniosoftware/invenio-records,inveniosoftware/invenio-search