箭头分离到独立的model中，方便自定义path

AIStudio.Wpf.DiagramDesigner/ViewModels/AdditionViewModel/Interface/IDrawModeViewModel.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace AIStudio.Wpf.DiagramDesigner
+{
+    public interface IDrawModeViewModel
+    {
+        DrawMode GetDrawMode();
+        void SetDrawMode(DrawMode drawMode);
+
+        void ResetDrawMode();
+
+        CursorMode CursorMode
+        { 
+            get; set; 
+        }
+
+        DrawMode LineDrawMode
+        { 
+            get; set;
+        }
+
+        RouterMode LineRouterMode
+        {
+            get; set;
+        }
+    }
+}