Add a facility to translate vtkPolyData to GeoJSON format.

GeoJSON is a specialization of JSON tailored to geodata.
This writer can write to a file or string and encodes geometry
topology and a single scalar attribute as a color for web visualization.

Change-Id: I68ff318c7c6a97bbdc8048e3b4068d51ae3d784f
Merge topic 'geojson_writer' into master

b4e358f6 Add a facility to translate vtkPolyData to GeoJSON format.