Make DistributionItem::P_IS_INITIALIZED private

GUI/Models/DistributionItems.h

@@ -24,9 +24,9 @@ class BA_CORE_API_ DistributionItem : public SessionItem {
 private:
     static const QString P_NUMBER_OF_SAMPLES;
     static const QString P_SIGMA_FACTOR;
+    static const QString P_IS_INITIALIZED;
 
 public:
-    static const QString P_IS_INITIALIZED;
     static const QString P_LIMITS;
     explicit DistributionItem(const QString& name);