Relationships from/to BAG pits rejected

[rutgervanwilligen]

Relationships rejected because BAG PiTs can't be found, while they should be present.

• [x] Find out why this happens
• [ ] Fix

[rutgervanwilligen]

Histograph/IO does not guarantee that PiTs are always put in the Redis queue imported before relations.

This will not be fixed -- it would be better to store all rejected relations in a separate place/database and add them later on.