Adaption of FreeCAD to QuarterWidget

-removes all soqtviewer references
-create a quarter adaptor class which implements missing functionality
-adopts freecad code to make use of SoRenderManager and changed View3DInventorViewer  interface

src/Gui/Clipping.cpp

@@ -128,7 +128,7 @@ Clipping::Clipping(Gui::View3DInventor* view, QWidget* parent)
     d->node->insertChild(d->clipZ, 0);
     d->node->insertChild(d->clipView, 0);
 
-    SoGetBoundingBoxAction action(viewer->getViewportRegion());
+    SoGetBoundingBoxAction action(viewer->getSoRenderManager()->getViewportRegion());
     action.apply(viewer->getSceneGraph());
     SbBox3f box = action.getBoundingBox();