Moved monthly/may flow into separate file and now populating flow data

The problem with SimpleFeatureCollection is that it suggests in a way that any feature collection will work (it won't because it needs to be of a particular feature type).  Also, we aren't doing anything with the geometries after this point, which is the main reason to leave it in a feature collection.  If you want to be more explicit about it, perhaps make a QwStation and FlowStation class and make it a Map<QwStation, FlowStation>.