Add GeoJSON capability

Supersedes pull request #760

Updated to meet Jordan’s expectation of only 1 new setting and no duplicated data.
Data can be in ‘geoip’ format (current default) with geoip.latitude & geoip.longitude
or
geojson format, which is ‘location’: [lon,lat].  This works for Kibana’s bettermap and for Elasticsearch’s geo_point format (with appropriate mapping).