Added IExecutable and ISlotContainer interface.

Changed SlotContainerNode to ExecutableNode

Runtime/Helpers/DataNodeExtension.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+
+namespace Misaki.GraphView
+{
+    public static class DataNodeExtension
+    {
+        public static void ClearAllExecuteFlag(this IList<DataNode> nodes)
+        {
+            foreach (var node in nodes)
+            {
+                if (node is IExecutable executable)
+                {
+                    executable.ClearExecutionFlag();
+                }
+            }
+        }
+    }
+}