MemorySessionStore: Session class added

MemorySessionStore$Session: clientSession field added
MemorySessionStore#pendingAck: secondPhaseStore & inflightStore &
inboundFlightMeessageToGuid added

ClientSession#cleanup missed these messages
SubscriptionsDirectoryTest: fixed
SessionsStore#dropInFlightMessagesInSession: changed to cleanSession

broker/src/main/java/io/moquette/server/netty/NettyMQTTHandler.java

@@ -86,6 +86,7 @@ public class NettyMQTTHandler extends ChannelInboundHandlerAdapter {
         } catch (Throwable ex) {
             LOG.error("Exception was caught while processing MQTT message, " + ex.getCause(), ex);
             ctx.fireExceptionCaught(ex);
+            ctx.close();
         }
     }