Make SphericalDetectorItem::P_PHI_AXIS private

GUI/Models/SphericalDetectorItem.h

@@ -20,8 +20,10 @@
 class BasicAxisItem;
 
 class BA_CORE_API_ SphericalDetectorItem : public DetectorItem {
-public:
+private:
     static const QString P_PHI_AXIS;
+
+public:
     static const QString P_ALPHA_AXIS;
     SphericalDetectorItem();