JSON->GeoJSON: If nodes/spans have bad geometries, don't include them in output data. Include info in meta.

[odscjames]

In Open-Telecoms-Data/cove-ofds#45 @lgs85 tried to some JSON data with a node with this location.

  "location": {
              "type": "Pint",
              "coordinates": [
                -0.174,
                5.625
              ]
            },

This produced dodgy output that crashes the map renderer.

The converter should check for bad location input and not process it, and include info on this bad input in the meta output.

(This issue can just be about "location" fields - there may be another issue wanted about what happens if other input data is bad, such as an organisation)

ps. Also related to #27