vidgrind: Geospatial search

[Alan Noble]

Permit geospatial search using location data extracted from MTS media metadata.

Proposal:

• Add a Geohash property to the MtsMedia entity.
• Upon entity insertion, either supply a geohash, or compute one from the latitude & longitude extracted from MTS metadata.
• Searching for MtsMedia at a given location is then transformed into a string search.

See also https://en.wikipedia.org/wiki/Geohash

Note that Google Cloud Datastore does not currently have built-in support for geospatial search.