cleanup of datacollectors and some examples

dune/vtk/CMakeLists.txt

dune/vtk/datacollectors/CMakeLists.txt

dune/vtk/datacollectors/continuousdatacollector.hh

dune/vtk/datacollectors/datacollectorinterface.hh

dune/vtk/datacollectors/discontinuousdatacollector.hh

dune/vtk/datacollectors/quadraticdatacollector.hh

dune/vtk/datacollectors/spdatacollector.hh

dune/vtk/datacollectors/structureddatacollector.hh

dune/vtk/datacollectors/unstructureddatacollector.hh

dune/vtk/datacollectors/yaspdatacollector.hh

dune/vtk/vtkfunction.hh

dune/vtk/vtktypes.cc

dune/vtk/vtkwriter.hh

dune/vtk/writers/CMakeLists.txt

dune/vtk/writers/vtkimagedatawriter.hh

dune/vtk/writers/vtkrectilineargridwriter.hh

dune/vtk/writers/vtkstructuredgridwriter.hh

dune/vtk/writers/vtkunstructuredgridwriter.hh

dune/vtk/writers/vtkwriterinterface.hh

src/CMakeLists.txt