Documentation - update programming example in Visualization user guide

// create a default display connection
Handle(Aspect_DisplayConnection) aDispConnection = new Aspect_DisplayConnection();
// create a Graphic Driver
Handle(OpenGl_GraphicDriver) aGraphicDriver = new OpenGl_GraphicDriver (aDispConnection);
// create a Viewer to this Driver
Handle(V3d_Viewer) VM = new V3d_Viewer (aGraphicDriver);
VM->SetDefaultBackgroundColor (Quantity_NOC_DARKVIOLET);
VM->SetDefaultViewProj (V3d_Xpos);
// Create a structure in this Viewer
Handle(Graphic3d_Structure) aStruct = new Graphic3d_Structure (VM->Viewer());
// Type of structure
aStruct->SetVisual (Graphic3d_TOS_SHADING);
// Create a group of primitives  in this structure
Handle(Graphic3d_Group) aPrsGroup = new Graphic3d_Group (aStruct);
// Fill this group with one quad of size 100
Handle(Graphic3d_ArrayOfTriangleStrips) aTriangles = new Graphic3d_ArrayOfTriangleStrips (4);
aTriangles->AddVertex (-100./2., -100./2., 0.0);
aTriangles->AddVertex (-100./2.,  100./2., 0.0);
aTriangles->AddVertex ( 100./2., -100./2., 0.0);
aTriangles->AddVertex ( 100./2.,  100./2., 0.0);
aPrsGroup->AddPrimitiveArray (aTriangles);
aPrsGroup->SetGroupPrimitivesAspect (new Graphic3d_AspectFillArea3d());
// Create Ambient and Infinite Lights in this Viewer
Handle(V3d_AmbientLight) aLight1 = new V3d_AmbientLight (VM, Quantity_NOC_GRAY50);
Handle(V3d_DirectionalLight) aLight2 = new V3d_DirectionalLight (VM, V3d_XnegYnegZneg, Quantity_NOC_WHITE);
// Create a 3D quality  Window with the same DisplayConnection
Handle(Xw_Window) aWindow = new Xw_Window (aDispConnection, "Test V3d", 0.5, 0.5, 0.5, 0.5);
// Map this Window to this screen
aWindow->Map();
// Create a Perspective  View in this Viewer
Handle(V3d_View) aView = new V3d_View (VM);
aView->Camera()->SetProjectionType (Graphic3d_Camera::Projection_Perspective);
// Associate this View with the Window
aView ->SetWindow (aWindow);
// Display ALL structures in this View
VM->Viewer()->Display();
// Finally update the Visualization in this View
aView->Update();
// Fit view to object size
V->FitAll();