Reorganize solution structure.

Source/MQTTnet/MqttApplicationMessage.cs

@@ -0,0 +1,15 @@
+using MQTTnet.Protocol;
+
+namespace MQTTnet
+{
+    public class MqttApplicationMessage
+    {
+        public string Topic { get; set; }
+
+        public byte[] Payload { get; set; }
+
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
+
+        public bool Retain { get; set; }
+    }
+}