Support name and lat/lng based resolution in dc-import tool

[pradh]

Just like how we support resolution by external ID (like isoCode) using ExternalIdResolver, we would like to support resolution by:

1. name property, using FindEntities recon API
2. latitude / longitude property pair, using coordinate recon API

This is so that datasets that identify a location by only name or its lat/lng can be transparently resolved without the user needing to do anything special.

For name recon it is important to carefully propagate resolution failures though!