This commmits intruduces a openturns modules and two filters
using openturns based on pdf computation.
The Kernel Smoothing Filter compute kernel smoothing on 1D data to be displayed in a line chart view
while the Density Map filter compute density maps on 2D data to be displayed in any type of chart views.
It also replace vtkScatterPlotMatrix with vtkOTScatterPlotMatrix
using a factory, in wich it can draw density maps

This also include some small modifications to vtkScatterPlotMatrix
to enable easy specialization of the class