0031570: Samples - add Qt samples similar to standard MFC samples

Added Qt sample OCCTOverview providing examples of use of OCCT API with relevant code and demonstration of results in the viewer.

Off-topic: some unused images are removed from dox/introduction/images/

samples/OCCTOverview/code/AdaptorPnt2d_AIS.cxx

@@ -0,0 +1,38 @@
+// Copyright (c) 2020 OPEN CASCADE SAS
+//
+// This file is part of the examples of the Open CASCADE Technology software library.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE
+
+#include "AdaptorPnt2d_AIS.h"
+
+#include <Geom_CartesianPoint.hxx>
+#include <StdPrs_Point.hxx>
+
+void AdaptorPnt2d_AIS::Compute (const Handle(PrsMgr_PresentationManager3d)& ,
+                                const Handle(Prs3d_Presentation)& thePrs,
+                                const Standard_Integer theMode)
+{
+  if (theMode != 0)
+  {
+    return;
+  }
+
+  Handle(Geom_CartesianPoint) aGeomPoint = new Geom_CartesianPoint(myPoint);
+  StdPrs_Point::Add (thePrs, aGeomPoint, myDrawer);
+}