Use ULID for ID fields instead of an int

> I think we should use ULIDs rather than plain IDs for future proofing. One of my “someday” projects is to work out how to move the other models to them.

Use:
https://github.com/valohai/ulid2/blob/master/README.md

Should be just a migration to change the ID fields on the models and replace the existing IDS.

"Just"...