Harvest_id column in jobs table should (maybe) be removed

The harvest_id column in historyinfo tabel gives potential risk of inconsistent data in case the value will differ from the value calculated via the jobs relation.
It should be checked why this column was introduced:
1. whether it is there for optimization reasons. In this case it should be investigated whether it is still relavant. If still relevant the documentation must be updated accordingly.
2. whether it is there for historic reasons that are not relevant anymore. In thsi case the column should be removed and code adjusted accordingly.