Some memory optimization for Arduino UNO following this thread:

https://community.openmqttgateway.com/t/arduino-uno-ethernet-shield-reboots-on-receiving-rf-signal-on-v-0-9/346/22
Rework led management to avoid use of global variables
and specify special JSON_MSG_BUFFER for arduino UNO
led can now be used for all the boards

generalize use of F macro
for memory optimization
change jsonbuffer calculation method
reduce pubsubclient max packet size for uno and nano

ZsensorBH1750.ino

@@ -55,7 +55,8 @@ void MeasureLightIntensity()
 {
   if (millis() > (timebh1750 + TimeBetweenReadingBH1750)) {//retriving value of Lux, FtCd and Wattsm2 from BH1750
     trc(F("Creating BH1750 buffer"));
-    StaticJsonBuffer<JSON_MSG_BUFFER> jsonBuffer;
+    const int JSON_MSG_CALC_BUFFER = JSON_OBJECT_SIZE(3);
+    StaticJsonBuffer<JSON_MSG_CALC_BUFFER> jsonBuffer;
     JsonObject& BH1750data = jsonBuffer.createObject();
     
     timebh1750 = millis();