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/ViewProviderCurvature.cpp

@@ -290,7 +290,7 @@ void ViewProviderMeshCurvature::updateData(const App::Property* prop)
     // set to the expected size
     if (prop->getTypeId().isDerivedFrom(App::PropertyLink::getClassTypeId())) {
         Mesh::Feature* object = static_cast<const App::PropertyLink*>(prop)->getValue<Mesh::Feature*>();
-        this->pcLinkRoot->removeAllChildren();
+        Gui::coinRemoveAllChildren(this->pcLinkRoot);
         if (object) {
             const Mesh::MeshObject& kernel = object->Mesh.getValue();
             pcColorMat->diffuseColor.setNum((int)kernel.countPoints());