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/MeshEditor.cpp

@@ -478,11 +478,11 @@ void MeshFillHole::startEditing(MeshGui::ViewProviderMesh* vp)
     myConnection = App::GetApplication().signalChangedObject.connect(
         boost::bind(&MeshFillHole::slotChangedObject, this, _1, _2));
 
-    myBoundariesRoot->removeAllChildren();
+    Gui::coinRemoveAllChildren(myBoundariesRoot);
     myBoundariesRoot->addChild(viewer->getHeadlight());
     myBoundariesRoot->addChild(viewer->getSoRenderManager()->getCamera());
     myBoundariesRoot->addChild(myBoundariesGroup);
-    myBoundaryRoot->removeAllChildren();
+    Gui::coinRemoveAllChildren(myBoundaryRoot);
     myBoundaryRoot->addChild(viewer->getHeadlight());
     myBoundaryRoot->addChild(viewer->getSoRenderManager()->getCamera());
     createPolygons();
@@ -541,7 +541,7 @@ void MeshFillHole::closeBridge()
 void MeshFillHole::slotChangedObject(const App::DocumentObject& Obj, const App::Property& Prop)
 {
     if (&Obj == myMesh && strcmp(Prop.getName(),"Mesh") == 0) {
-        myBoundariesGroup->removeAllChildren();
+        Gui::coinRemoveAllChildren(myBoundariesGroup);
         myVertex->point.setNum(0);
         myNumPoints = 0;
         myPolygon.clear();

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());

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);