workflows: add OAIHarvest integration
- Refactors log messages in generic harvesting workflow tasks.
- Adds a new task to convert records with information directly from OAI repository models.
- Generic workflow now takes parameter of the given repository.
- Cleans the code of several functions, simplifies the harvesting a bit. Changes the way the updating of the last_time update.
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>