[src] minor bugfix in computePDF method
[test] Minor bugfix in sum of characteristic functions evaluations
[src] Fixed the computeEquivalentNormalPDFSum method: we should take into account all 1D/2D/3D faces and not only corners.
For that purposes, the get_points_on_grid_pdf_ method has been implemented in
order to get the list of points for each computeEquivalentNormalPDFSum's
iteration. The number of points increase with the iteration number
Need elementary validations
[test] Added test script for validation of get_points_on_grid_pdf_ method. Both number of points and unicity are checked in dimensions 1, 2 and 3