Added the functionality to add RelayNode directly to edge between two Prot;

Editor/Contracts/IDataNodeView.cs

@@ -0,0 +1,22 @@
+namespace Misaki.GraphView.Editor
+{
+    public interface IDataNodeView<T> : IDataNodeView
+    {
+        /// <summary>
+        /// The data node that the view represents.
+        /// </summary>
+        public T DataNode
+        {
+            get;
+        }
+    }
+
+    public interface IDataNodeView
+    {
+        /// <summary>
+        /// Get the data node that the view represents.
+        /// </summary>
+        /// <returns></returns>
+        public DataNode GetDataNode();
+    }
+}