Make SpecularDataItem::P_TITLE private

GUI/coregui/Models/SpecularDataItem.h

@@ -26,8 +26,10 @@ const QString y_axis_default_name = "Signal [a.u.]";
 } // namespace SpecularDataAxesNames
 
 class BA_CORE_API_ SpecularDataItem : public DataItem {
-public:
+private:
     static const QString P_TITLE;
+
+public:
     static const QString P_XAXIS;
     static const QString P_YAXIS;