New config option for OAI-PMH Harvester

Adds configurable option to OAI-PMH harvester to allow sets to be part of the OID generation algorithm. Helps if overlapping sets in remote repo cause objects to be overwritten. Also adds ignore for intelliJ project files.

Particularly useful (for example) if you want to harvest RECORDS from the NLA Party Infrastructure (RECORDS = OAI Sets), since the OAI IDs are for the parent IDENTITIES, so if two RECORDS are from the same IDENTITY this allows TF2 to harvest each record into two objects.

Defaults to 'false', so no negative impacts on current users I would hope.