[Paraview] name blocks or sets and export them in X3D files

[Kristian Sons]

Hi Pierre,

though Berk answered your questions already, Christophe Mouton from EDF
asked me to add some details.
I contributed the rewrite of the X3D exporter and the binary X3D exporter
on behalf of EDF.

The X3D exporter is not aware of the composite data types of VTK. It works
roughly like this:

1. Get all the actors from a vtkRenderWindow (it implements the vtkExporter
interface)
2. Each Actor is mapped to a X3D <Shape>
3. Each vtkProperty/vtkTexture is mapped to a X3D <Appearance>, <Material>,
<PixelTexture>
4. Each geometry is either a vtkPolyData or is converted to vtkPoylData
using the vtkGeometryFilter
5. The vtkPolyData is mapped to X3D <IndexedFaceSet>, <LineSet>, <PointSet>

It's generally not a big task to add composite support to the exporter, the
Appearance could be reused using the USE/DEF semantic of X3D.

Best regards,
Kristian