Start vtkGeoJSONMapFeature class to bring GeoJSON features to vtkMap

Requires including vtkDataSetReaders, which is at:
  https://github.com/OpenGeoscience/vtkDataSetReaders
Also note that vtkGeoJSONFeature class already used in vtkDataSetReaders
First GeoJSON test case - polygon spanning central New York
Add test cases for GeoJSON MultiLineString and Point features
Add vtkMap::FindLayer() method.

Also fix error in ny-points.geojson test file.
Also update readme file to indicate the vtkDataSetReaders requirement.
Merge branch 'master' into john/geojson-feature

Resolved conflicts in:
	Testing/CMakeLists.txt
Merge pull request #56 from OpenGeoscience/john/geojson-feature

John/geojson feature