use ClusterPrefab instead of Cluster

Runtime/Scripts/Core/Neuron.cs

@@ -88,6 +88,14 @@ namespace NanoBrain {
             return null;
         }
 
+        public Synapse GetSynapse(string senderNeuronName) {
+            Neuron sender = this.parent.GetNeuron(senderNeuronName);
+            if (sender == null)
+                return null;
+            
+            return this.GetSynapse(sender);
+        }
+
         /// <summary>
         /// Remove a synapse from a Nucleus
         /// </summary>