update converter to accept data aggregated from multiple agencies

[ryanbranciforte]

Ex. I am working with data that has been aggregated in Ohio. The shapefile contains a "steward" field indicating the separate agencies.

[geobrando]

👍

Not sure how common this is, but I also have some aggregated data from a parks committee composed of trails from multiple stewards. Converter could detect this field and allow user to confirm or could prompt user to specify the field explicitly. In my dataset, the field is named "MAINTENANC"