Reference feature finder application

[ksonda]

Per discussion with @dblodgett-usgs on slack, our preference for data providers is to go through something like this algorithm:

1. Determine if my sites are already reference features (gages, dams, PWS, wells, etc.)
2. If yes, rather than mint PIDs for locations, make dataset landing pages, which are schema:about or sosa:FeatureOfInterest to reference PIDs
3. If no: contribute sites to references features, and then do (2)

To do this, we need an easy way for people to identify which reference features, if any, correspond to their sites. Suggest a workflow where:

User submits a file or API endpoint of their sites, perhaps selects a reference feature collection, and retrieves a csv of their site identifiers and 1-5 potential matches to reference PIDs, perhaspw tih a score or distance metric. Also an html map may be helfpul

[ksonda]

Subsumes #160