renamed Serializer -> (onlab.netty-layer) PayloadSerializer

- Added TODO memos to ClusterCommunicationService layer

Change-Id: I4c81a72d03cddd23637f9c6cbf102125ea448c01
diff --git a/utils/netty/src/main/java/org/onlab/netty/MessageEncoder.java b/utils/netty/src/main/java/org/onlab/netty/MessageEncoder.java
index 5581747..0ee29cb 100644
--- a/utils/netty/src/main/java/org/onlab/netty/MessageEncoder.java
+++ b/utils/netty/src/main/java/org/onlab/netty/MessageEncoder.java
@@ -17,10 +17,10 @@
     public static final int SERIALIZER_VERSION = 1;
 
 
-    private final Serializer serializer;
+    private final PayloadSerializer payloadSerializer;
 
-    public MessageEncoder(Serializer serializer) {
-        this.serializer = serializer;
+    public MessageEncoder(PayloadSerializer payloadSerializer) {
+        this.payloadSerializer = payloadSerializer;
     }
 
     @Override
@@ -35,12 +35,12 @@
         // write preamble
         out.writeBytes(PREAMBLE);
 
-        byte[] payload = serializer.encode(message);
+        byte[] payload = payloadSerializer.encode(message);
 
         // write payload length
         out.writeInt(payload.length);
 
-        // write serializer version
+        // write payloadSerializer version
         out.writeInt(SERIALIZER_VERSION);
 
         // write payload.