Added IExecutable and ISlotContainer interface.

Changed SlotContainerNode to ExecutableNode

Runtime/Contracts/Nodes/ISlotContainer.cs

@@ -0,0 +1,30 @@
+namespace Misaki.GraphView
+{
+    public interface ISlotContainer
+    {
+        /// <summary>
+        /// Add the slot to the container.
+        /// </summary>
+        /// <param name="slot"> <see cref="Slot"/> The slot want to add </param>
+        public void AddSlot(Slot slot);
+        
+        /// <summary>
+        /// Remove the slot from the container.
+        /// </summary>
+        /// <param name="slot"> <see cref="Slot"/> The slot want to remove </param>
+        public void RemoveSlot(Slot slot);
+
+        /// <summary>
+        /// Get the slot by the index and direction.
+        /// </summary>
+        /// <param name="index"> <see cref="int"/> Index of the slot</param>
+        /// <param name="direction"> <see cref="SlotDirection"/> Direction of the slot </param>
+        /// <returns> <see cref="Slot"/> The slot that matches the index and direction </returns>
+        public Slot GetSlot(int index, SlotDirection direction);
+
+        /// <summary>
+        /// Unlink all the slots of the node.
+        /// </summary>
+        public void UnlinkAllSlots();
+    }
+}