BibTasklets: update APS harvest conversion

* Updates the APS harvest tasklet to convert using the new
  ApsPackage available from Harvesting Kit.

* Refactors the threshold date checking as APS has changed
  their format.

* Updates harvesting functions as APS has updated their REST
  API.

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