BibRecord: filter field instances

• Introduces new function for filtering field instances obtained from record. Function returns only those field instances that match some-other-subfield/some-other-value criteria. The function can work in 'exact', 'substring' and 'regex' mode. (addresses #1550)

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>