Gui: disable lighting for the label of an axis

This way the backside of the label is displayed with the same color as the front side. Otherwise it may be black.

src/Gui/ViewProviderOrigin.cpp

@@ -24,7 +24,8 @@
 #include "PreCompiled.h"
 
 #ifndef _PreComp_
-# include <Inventor/nodes/SoGroup.h>
+# include <Inventor/nodes/SoLightModel.h>
+# include <Inventor/nodes/SoSeparator.h>
 #endif
 
 #include <App/Document.h>
@@ -59,6 +60,10 @@ ViewProviderOrigin::ViewProviderOrigin()
 
     pcGroupChildren = new SoGroup();
     pcGroupChildren->ref();
+
+    auto lm = new SoLightModel();
+    lm->model = SoLightModel::BASE_COLOR;
+    pcRoot->insertChild(lm, 0);
 }
 
 ViewProviderOrigin::~ViewProviderOrigin() {