POI IDs not always the same for the same location / flowpath outflow

@abock - following on our slack conversation:

Right now, we are assuming all POIs are "outflows". This will change, but for now there are instances (34 in VPU01) where more then one POI_ID is assigned to the same flowpath ID. The intention of the POI_ID (in my understanding) is that it provides a globally unique identifier based on a location (in this case the outlet of said flowpath). That POI_ID can then be associate with many POI reference/links.