Fall-back Offer per Placement

[#1]

Currently there is only one fall-back Offer per decision, even if in the decision there are multiple Placements involved. It should be possible to indicate a fall-back Offer per Placements.

If there is more than 1 Placement involved in a decision but there is only 1 fall-back Offer per decision, it means that some Placements will not be used as a potetial promotion. This can be sub-optimal in the communication strategy towards the customers.