OAIHarvest: improves arXiv identifier harvesting

• When specifying identifiers on the command line to oaiharvest, you can now specify the short-hand arXiv identifier instead of the full OAI identifier.
  
  BEWARE: Special INSPIRE use-case only as assumptions that arXiv is the only OAI source is being made at this point.

• Removes some INSPIRE specific code to keep track of authorlists.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>