BibKnowledge: optional memoisation of KBR lookups

• Offers optional memoisation of KBR lookups. Beware, the memoised cache is not automatically updated if the KB changes. Hence this is useful for short-lived CLI processes, not for long-lived WSGI processes. (addresses #1484)

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