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/Robot/Gui/ViewProviderRobotObject.cpp

@@ -111,7 +111,7 @@ void ViewProviderRobotObject::setDragger()
 void ViewProviderRobotObject::resetDragger()
 {
     assert(pcDragger);
-    pcTcpRoot->removeAllChildren();
+    Gui::coinRemoveAllChildren(pcTcpRoot);
     pcDragger = 0;
 }
 
@@ -181,7 +181,7 @@ void ViewProviderRobotObject::updateData(const App::Property* prop)
         QString fn = QString::fromUtf8(filename);
         QFile file(fn);
         SoInput in;
-        pcRobotRoot->removeAllChildren();
+        Gui::coinRemoveAllChildren(pcRobotRoot);
         if (!fn.isEmpty() && file.open(QFile::ReadOnly)) {
             QByteArray buffer = file.readAll();
             in.setBuffer((void *)buffer.constData(), buffer.length());