0030599: Visualization - implement StdPrs_SectionLines tool

0030599: Visualization - implement StdPrs_SectionLines tool

StdPrs_SectionLines tool is implemented: it is possible to compute a cross section of the shape with the plane.
# Some features have not been implemented yet:
#   * the method StdPrs_SectionLines::Add() that should add objects inside section to the Prs3d_Presentation;
#   * corresponding Draw Harness command;
#   * interactive object that could represent the cross section;
#   * triangles that lie inside the section plane have not been processed yet.