Make Data1DViewItem::P_TITLE private

GUI/Models/Data1DViewItem.h

@@ -30,8 +30,10 @@ template <class T> class OutputData;
 //! items determines axes' limits.
 
 class BA_CORE_API_ Data1DViewItem : public SessionItem {
-public:
+private:
     static const QString P_TITLE;
+
+public:
     static const QString P_XAXIS;
     static const QString P_YAXIS;
     static const QString P_AXES_UNITS;