Revamp code

-Move MoveElementsCommand class from diagramcommands file to
movegraphicsitemcommand file.
-Rename the to class MoveGraphicsItemCommand.
-Minor code change to make it more modern.

sources/diagramcommands.h

@@ -69,45 +69,6 @@ class CutDiagramCommand : public DeleteQGraphicsItemCommand {
 	CutDiagramCommand(const CutDiagramCommand &);
 };
 
-/**
-	@brief The MoveElementsCommand class
-	This command moves some content on a particular diagram.
-*/
-class MoveElementsCommand : public QUndoCommand {
-		// constructors, destructor
-	public:
-		MoveElementsCommand(Diagram *, const DiagramContent &,
-				    const QPointF &m, QUndoCommand * = nullptr);
-		~MoveElementsCommand() override;
-	private:
-		MoveElementsCommand(const MoveElementsCommand &);
-	
-		// methods
-	public:
-		void undo() override;
-		void redo() override;
-		virtual void move(const QPointF &);
-
-	private:
-		void setupAnimation (QObject * target,
-				     const QByteArray &propertyName,
-				     const QVariant& start,
-				     const QVariant& end);
-	
-	// attributes
-	private:
-	/// diagram the movement takes place on.
-	Diagram *diagram;
-	/// moved content
-	DiagramContent content_to_move;
-	/// applied movement
-	QPointF movement;
-	///animation group
-	QParallelAnimationGroup *m_anim_group;
-	/// prevent the first call to redo()
-	bool first_redo;
-};
-
 /**
 	@brief The MoveConductorsTextsCommand class
 	This command moves text items related to conductors