Big refactory on session management:

- introduced a unique point of access and management of sessions state (SessionRepository)
- separated behaiour for sessions with clean flag to false into DurableSession
- separated behaviour for session with clean flag to true into TransientSession

broker/src/main/java/io/moquette/spi/EnqueuedMessage.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2012-2017 The original author or authors
+ * ------------------------------------------------------
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * and Apache License v2.0 which accompanies this distribution.
+ *
+ * The Eclipse Public License is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * The Apache License v2.0 is available at
+ * http://www.opensource.org/licenses/apache2.0.php
+ *
+ * You may elect to redistribute this code under either of these licenses.
+ */
+
+package io.moquette.spi;
+
+public class EnqueuedMessage {
+
+    public final IMessagesStore.StoredMessage msg;
+    public final int messageId;
+
+    EnqueuedMessage(IMessagesStore.StoredMessage msg, int messageId) {
+        this.msg = msg;
+        this.messageId = messageId;
+    }
+}