箭头分离到独立的model中，方便自定义path

AIStudio.Wpf.DiagramDesigner.Demo/ViewModels/ZoomViewModel.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Windows;
+
+namespace AIStudio.Wpf.DiagramDesigner.Demo.ViewModels
+{
+    class ZoomViewModel : BaseViewModel
+    {
+        public ZoomViewModel()
+        {
+            Title = "Zoom";
+            Info = "Drag the upper-right scroll bar to make the canvas larger and smaller.";
+
+            _service.ColorViewModel.FillColor.Color = System.Windows.Media.Colors.Orange;
+
+            DiagramViewModel = new DiagramViewModel();
+            DiagramViewModel.PageSizeType = PageSizeType.Custom;
+            DiagramViewModel.PageSize = new Size(double.NaN, double.NaN);
+
+            DefaultDesignerItemViewModel node1 = new DefaultDesignerItemViewModel() { Left = 50, Top = 50, Text = "1" };
+            DiagramViewModel.DirectAddItemCommand.Execute(node1);
+
+            DefaultDesignerItemViewModel node2 = new DefaultDesignerItemViewModel() { Left = 300, Top = 300, Text = "2" };
+            DiagramViewModel.DirectAddItemCommand.Execute(node2);
+
+            DefaultDesignerItemViewModel node3 = new DefaultDesignerItemViewModel() { Left = 300, Top = 50, Text = "3" };
+            DiagramViewModel.DirectAddItemCommand.Execute(node3);
+
+            ConnectionViewModel connector1 = new ConnectionViewModel(node1.RightConnector, node2.LeftConnector, DrawMode.ConnectingLineSmooth, RouterMode.RouterNormal);
+            DiagramViewModel.DirectAddItemCommand.Execute(connector1);
+
+            ConnectionViewModel connector2 = new ConnectionViewModel(node2.RightConnector, node3.RightConnector, DrawMode.ConnectingLineStraight, RouterMode.RouterOrthogonal);
+            DiagramViewModel.DirectAddItemCommand.Execute(connector2);
+
+        }
+    }
+}