Gui: add coinRemoveAllChildren to work around Coin3D bug

See bug description:
https://bitbucket.org/Coin3D/coin/pull-requests/119/fix-sochildlist-auditing/diff

Because of path based rendering (SoFCPathAnnotation) in mouse over
highlight, this bug causes crash more frequently here comparing to
upstream.

All C++ calling of SoGroup::removeAllChildren() is replaced by
Gui::coinRemoveAllChildren(), and python code is fixed by monkey
patching SoGroup.removeAllChildren() in FreeCADGuiInit.py.

src/Mod/Part/Gui/ViewProviderSpline.cpp

@@ -93,7 +93,7 @@ void ViewProviderSpline::updateData(const App::Property* prop)
     if (prop->getTypeId() == Part::PropertyPartShape::getClassTypeId() && strcmp(prop->getName(), "Shape") == 0) {
         // update control points if there
         if (pcControlPoints) {
-            pcControlPoints->removeAllChildren();
+            Gui::coinRemoveAllChildren(pcControlPoints);
             showControlPoints(this->ControlPoints.getValue(), prop);
         }
     }