Fix Qt 6 definition of macro ‘Q_DECLARE_MOVABLE_CONTAINER’

adding #include <QHash>

+ code fail to compile if it uses deprecated APIs.
=> see .pro file

sources/undocommand/deleteqgraphicsitemcommand.h

@@ -1,17 +1,17 @@
 /*
 	Copyright 2006-2020 The QElectroTech Team
 	This file is part of QElectroTech.
-	
+
 	QElectroTech is free software: you can redistribute it and/or modify
 	it under the terms of the GNU General Public License as published by
 	the Free Software Foundation, either version 2 of the License, or
 	(at your option) any later version.
-	
+
 	QElectroTech is distributed in the hope that it will be useful,
 	but WITHOUT ANY WARRANTY; without even the implied warranty of
 	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 	GNU General Public License for more details.
-	
+
 	You should have received a copy of the GNU General Public License
 	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
 */
@@ -19,6 +19,8 @@
 #define DELETEQGRAPHICSITEMCOMMAND_H
 
 #include <QUndoCommand>
+#include <QHash>
+
 #include "diagramcontent.h"
 
 class Diagram;
@@ -32,17 +34,17 @@ class DeleteQGraphicsItemCommand : public QUndoCommand
 	public:
 		DeleteQGraphicsItemCommand(Diagram *diagram, const DiagramContent &content, QUndoCommand * parent = nullptr);
 		~DeleteQGraphicsItemCommand() override;
-		
+
 	private:
 		DeleteQGraphicsItemCommand(const DeleteQGraphicsItemCommand &);
-		
+
 		void setPotentialsOfRemovedElements();
 		Terminal *terminalInSamePotential(Terminal *terminal, Conductor *conductor_to_exclude);
 
 	public:
 		void undo() override;
 		void redo() override;
-		
+
 		// attributes
 	private:
 		DiagramContent m_removed_contents;