OAIHarvest: configurable selective post-processing

• Allow to selectively apply post-processing phases to each individual harvested record. To do so override function oai_harvest_templates.tmpl_should_process_record_with_mode(). (closes #1477)

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Acked-by: Jan Aage Lavik <jan.age.lavik@cern.ch>