Merged topic subscription search and publish into single MessagePublisher method

First step on implementing H2 storage

Minor, fixed not imported class

Cleaned MessageStore interface to avoid duplication of methods used in couple. Switched from guid + message to move messages

Separated ISubscriptionsStore from ISessionStore

Implemented H2 queue

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

@@ -18,9 +18,21 @@ package io.moquette.spi;
 
 public interface IStore {
 
-    IMessagesStore messagesStore();
-
-    ISessionsStore sessionsStore();
+    void initStore();
 
     void close();
+
+    /**
+     * Factory method to instantiate the messages store.
+     *
+     * @return the create instance of IMessagesStore.
+     * */
+    IMessagesStore messagesStore();
+
+    /**
+     * Factory method to instantiate the session store.
+     *
+     * @return the create instance of ISessionsStore.
+     * */
+    ISessionsStore sessionsStore();
 }