mqtt refactoring, change version to 1.4.0-rc.1

* added MqttWriter
* added MqttWiFiClient (modified WiFiClient for esp8266)
* adaptation HomeAssistantHelper for MqttWriter
* adaptation HaHelper for new HomeAssistantHelper

lib/MqttWriter/MqttWiFiClient.h

@@ -0,0 +1,24 @@
+#include <WiFiClient.h>
+
+class MqttWiFiClient : public WiFiClient {
+public:
+#ifdef ARDUINO_ARCH_ESP8266
+  void flush() override {
+    if (this->connected()) {
+      WiFiClient::flush(0);
+    }
+  }
+
+  void stop() override {
+    this->abort();
+  }
+#endif
+
+#ifdef ARDUINO_ARCH_ESP32
+  void setSync(bool) {}
+
+  bool getSync() {
+    return false;
+  }
+#endif
+};