Mqtt discovery (#320)

* add mqtt discovery (compatibile with home assistant) with omg status binary sensor & bme280 sensor

* added mqtt discovery to Test_config.h for ESP32 (ESP8266 & other boards was not tested)

* include support for ESP8266 & arduino mega

* fix getting MAC for esp8266

* esp8266 fix

* make mqtt discovery functions functions more generic, readable and easy to use & extend

* make mqtt discovery functions functions more generic, readable and easy to use & extend PART 2

* remove the macro for each attribute and supposing that if there is a bme280 we expose all

OpenMQTTGateway.ino

@@ -133,6 +133,9 @@
 #ifdef ZsensorGPIOKeyCode
   #include "config_GPIOKeyCode.h"
 #endif
+#ifdef ZmqttDiscovery
+  #include "config_mqttDiscovery.h"
+#endif
 
 /*------------------------------------------------------------------------*/
 
@@ -193,7 +196,7 @@ void saveConfigCallback () {
 }
 
 boolean reconnect() {
-  
+
   // Loop until we're reconnected
   while (!client.connected()) {
       trc(F("MQTT connection...")); //F function enable to decrease sram usage
@@ -204,6 +207,11 @@ boolean reconnect() {
       pub(will_Topic,Gateway_AnnouncementMsg,will_Retain);
       // publish version
       pub(version_Topic,OMG_VERSION,will_Retain);
+      //home assistant discovery
+      #ifdef ZmqttDiscovery
+      pubMqttDiscovery();
+      #endif
+
       //Subscribing to topic
       if (client.subscribe(subjectMQTTtoX)) {
         #ifdef ZgatewayRF
@@ -783,6 +791,9 @@ void stateMeasures(){
       #ifdef ZsensorGPIOKeyCode
           modules = modules  + ZsensorGPIOKeyCode;
       #endif
+      #ifdef ZmqttDiscovery
+          modules = modules  + ZmqttDiscovery;
+      #endif
       SYSdata["modules"] = modules;
       trc(modules);
       char JSONmessageBuffer[100];