Clean up POI and event handling.

The event handling needs to be pulled up to navigate rather than doing it in refactor. I left a FIXME in 05_refactor_flowlines for it.

From what I've done so far, we need to move the POI event determination up into navigate and pass that information along in the POI table in the reference fabric.

Specifically, this https://code.usgs.gov/wma/nhgf/gfv2.0/-/blob/main/workspace/05_hyRefactor_flines.Rmd#L65 needs to move up to navigate. Ideally, this would be in a function that handles which events to split and which to leave alone. I think it would be best to do that before some of the POI moving stuff?

This also needs to be moved out into a function and called in navigate. https://code.usgs.gov/wma/nhgf/gfv2.0/-/blob/main/workspace/06-2_aggregate_cats.Rmd#L54

Another side issue is the handling of inferred POIs that get generated here: https://code.usgs.gov/wma/nhgf/gfv2.0/-/blob/main/workspace/06-2_aggregate_cats.Rmd#L155 these end up with NA ids and no other information in the final_POIs. That needs to be cleaned up.

@abock -- do you want to take this one on? I'm not going to have time and it would be good to tackle this sooner than later.