Removed vtkSource, vtkProcessObject and subclasses.
First step in the removal of VTK 4 compatibility layer. I removed vtkSource, vtkProcessObject and all of their subclasses. All algorithms should be subclasses of vtkAlgorithm now. Also removed vtkPLOT3DReader. This reader was using legacy API. Use vtkMultiBlockPLOT3DReader instead Made changes vtkSpatialRepresentationFilter that are not backwards compatible. This filter now produces a multi-block output and which levels are computed is controlled using the AddLevel method.