0029750: Samples - function arrows are not updated by moving a node in FuncDemo qt sample

The visual links between functions are recovered.
The demo is synchronized with a corresponding demo from Qt (qt486-vc10-32\examples\graphicsview\elasticnodes). It may be successfully compiled by any further versions of Qt including 5.10.1
Also, because Open CASCADE (and OCAF in particular) is improved for usage in multi-threading mode, usage of mutexes is added in this sample (for access to the sharing TNaming_UsedShapes attribute, for example).

samples/qt/FuncDemo/src/ShapeSaverDriver.cpp

@@ -56,10 +56,14 @@ Standard_Integer ShapeSaverDriver::Execute(Handle(TFunction_Logbook)& log) const
         }
     }
 
-    //BRepTools::Write(C, "result.brep");
+    if (myMutex)
+        myMutex->Lock();
 
     TNaming_Builder Bui(Label());
     Bui.Generated(C);
 
+    if (myMutex)
+        myMutex->Unlock();
+
     return BaseDriver::Execute(log);
 }