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/impl/Qos1PublishHandler.java

@@ -93,7 +93,7 @@ class Qos1PublishHandler extends QosPublishHandler {
                 throw new RuntimeException("Internal bad error, found connectionDescriptors to null while it should " +
                     "be initialized, somewhere it's overwritten!!");
             }
-            LOG.debug("clientIDs are {}", connectionDescriptors);
+            LOG.trace("connected clientIDs are {}", connectionDescriptors.getConnectedClientIds());
             if (!connectionDescriptors.isConnected(clientId)) {
                 throw new RuntimeException(String.format("Can't find a ConnectionDescriptor for client %s in cache %s",
                     clientId, connectionDescriptors));