Add isFull method to check slave limit

Added a new method to check if the slave limit is reached.

sources/qetgraphicsitem/masterelement.h

@@ -44,6 +44,8 @@ class MasterElement : public Element
 		void unlinkElement     (Element *elmt) override;
 		void initLink          (QETProject *project) override;
 		QRectF XrefBoundingRect() const;
+
+		bool isFull() const; // NEU: Prüft, ob das Slave-Limit erreicht ist
 		
 	protected:
 		QVariant itemChange(