qmqtt_client.h/publish() - add namespace to message parameter

Avoid collisions with eventual other 'Message' classes.

src/mqtt/qmqtt_client.h

@@ -190,7 +190,7 @@ public slots:
     void subscribe(const QString& topic, const quint8 qos = 0);
     void unsubscribe(const QString& topic);
 
-    quint16 publish(const Message& message);
+    quint16 publish(const QMQTT::Message& message);
 
 signals:
     void connected();