Better sensors (#154)

* globally expose repeat functionality as advanced function

* implement repeated sends for Arduino based boards

* use String class instead of C-style arrays to benefit from dynamic allocation and avoid buffer overflows. Try to improve stability of BME280.

* replace sprintf with String class to avoid buffer overruns by dynamic allocation

* fix caps on variable

* re-add TSL2561 code that was accidentally removed

OpenMQTTGateway.ino

@@ -241,6 +241,9 @@ void setup()
   #ifdef ZsensorBH1750
     setupZsensorBH1750();
   #endif
+  #ifdef ZsensorTSL2561
+    setupZsensorTSL2561();
+  #endif
   #ifdef ZgatewayIR
     setupIR();
   #endif
@@ -373,6 +376,9 @@ void loop()
     #ifdef ZsensorBH1750
       MeasureLightIntensity(); //Addon to measure Light Intensity with a BH1750
     #endif
+    #ifdef ZsensorTSL2561
+      MeasureLightIntensityTSL2561();
+    #endif
     #ifdef ZsensorDHT
       MeasureTempAndHum(); //Addon to measure the temperature with a DHT
     #endif