Added initial Melody Playback Ability

Now, controlled via MQTT a Playback of a melody can Start, Stop, Pause 
etc. 

Settings like speed, total duration, pauses etc can be set.

MQTT_Message_Handling.hpp

@@ -0,0 +1,81 @@
+#pragma once
+
+void handlePlaybackCommands(char * command);
+
+void handleJSON(char * payload) {
+	JsonDocument doc;
+	DeserializationError error = deserializeJson(doc, payload);
+
+	if (error) {
+		Serial.print("deserializeJson() failed: ");
+		Serial.println(error.c_str());
+		return;
+	}
+
+	setMelodyAttributes(doc);
+	loadMelodyInRAM(melody_steps);
+}
+
+void SuscribeMqtt() {
+
+	  String topicPlayback = String("vesper/") + DEV_ID + "/control/playback";
+    String topicSetMelody = String("vesper/") + DEV_ID + "/control/setMelody";
+    String topicAddMelody = String("vesper/") + DEV_ID + "/control/add_melody";
+
+    uint16_t control_id = mqttClient.subscribe(topicPlayback.c_str(), 2);
+    Serial.print("Subscribing to Playback Control topic, QoS 2, packetId: ");
+    Serial.println(control_id);
+
+	uint16_t set_melody_id = mqttClient.subscribe(topicSetMelody.c_str(), 2);
+    Serial.print("Subscribing to Set-Melody topic, QoS 2, packetId: ");
+    Serial.println(set_melody_id);
+
+	// doesn't work yet:
+    uint16_t add_melody_id = mqttClient.subscribe(topicAddMelody.c_str(), 2);
+    Serial.print("Subscribing to Add-Melody topic, QoS 2, packetId: ");
+    Serial.println(add_melody_id);
+
+}
+
+void OnMqttReceived(char * topic, char * payload, AsyncMqttClientMessageProperties properties, size_t len, size_t index, size_t total) {
+
+	String topicPlayback = String("vesper/") + DEV_ID + "/control/playback";
+  String topicSetMelody = String("vesper/") + DEV_ID + "/control/setMelody";
+  String topicAddMelody = String("vesper/") + DEV_ID + "/control/add_melody";
+
+
+	//String payloadContent = String(payload).substring(0, len);
+
+	if (String(topic) == topicPlayback){
+		handlePlaybackCommands(payload);
+	}
+
+	else if (String(topic) == topicSetMelody) {
+		handleJSON(payload);
+	}
+
+	else if (String(topic) == topicAddMelody) {
+		// Handle adding melody
+		Serial.println("Adding melody...");
+		// You can call a function here to handle adding the melody
+	}
+	else {
+		// Handle unknown topics
+		Serial.println("Unknown topic received.");
+	}
+}
+
+// void PublishMqtt(unsigned long data) {
+//
+// 	//Doesn't publish anything yet.
+// 	String topicData = String("vesper/") + DEV_ID + "/data";
+// 	String payload = String(data);
+// 	mqttClient.publish(topicData.c_str(), 0, true, (char*)payload.c_str());
+//
+// }
+
+
+void PublishMqtt(const char *data) {
+    String topicData = String("vesper/") + DEV_ID + "/data";
+    mqttClient.publish(topicData.c_str(), 0, true, data);
+}