Feature/geojson (#2595)

Add the option to add geojson components to globes, from geojson files. One geojson file creates one GeoJsonComponent, which in turn may contain multiple GlobeGeometryFeatures

Geojson is a format that supports points, lines, and polygons. In addition to the basic functionality, extra features have been added that will long-term allow rendering the geometry needed to represent KML files (another format for geospatial geometry data). Here are links to references for both formats:

    Geojson: https://geojson.org/
    KML: https://developers.google.com/kml/documentation/kmlreference

data/assets/examples/geojson includes some example files that I have used for testing. Any geojson file can also be added through drag-n-drop. Note however that you might need to change the AltitudeMode or HeightOffset properties for the feature to be visible.

scripts/drag_drop_handler.lua

@@ -46,4 +46,6 @@ elseif extension == ".asset" then
     openspace.asset.add("]] .. filename .. '");' .. ReloadUIScript
 elseif extension == ".osrec" or extension == ".osrectxt" then
   return 'openspace.sessionRecording.startPlayback("' .. filename .. '")'
+elseif extension == ".geojson" then
+  return 'openspace.globebrowsing.addGeoJsonFromFile("' .. filename .. '")'  .. ReloadUIScript
 end