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/Mesh/Gui/ViewProviderMeshFaceSet.cpp

@@ -154,7 +154,7 @@ void ViewProviderMeshFaceSet::updateData(const App::Property* prop)
 
         if (direct != directRendering) {
             directRendering = direct;
-            pcShapeGroup->removeAllChildren();
+            Gui::coinRemoveAllChildren(pcShapeGroup);
 
             if (directRendering) {
                 pcShapeGroup->addChild(pcMeshNode);