**What**
- Adjust reservations correctly according to the following heuristic:
adjustment by addition: (i.e. positive quantity adjustment passed to the adjustment method)
- if a reservation for the line-item in the location exists add quantity to that
- if not create a new reservation
adjustment by subtraction:
- if a reservation with the exact quantity exists, delete it and return
- if a reservation with a greater quantity exists, subtract from it and return
- otherwise delete from reservations until a reservation with greater quantity than the remaining is found and adjust that with the remaining quantity OR there are no more reservations
Fixes CORE-1247
02c77d7059