Support LM75 temperature sensor (#1327)

* First draft of LM75 sensor based on HTU21 sensor

* Initialise I2C on ESP8266

* Add LM75 sensor to test builds

So that it will be tested with the continuous integration

main/User_config.h

@@ -315,6 +315,7 @@ int lowpowermode = DEFAULT_LOW_POWER_MODE;
 //#define ZsensorTSL2561 "TSL2561"  //ESP8266, Arduino, ESP32
 //#define ZsensorBME280  "BME280"   //ESP8266, Arduino, ESP32
 //#define ZsensorHTU21   "HTU21"    //ESP8266, Arduino, ESP32
+//#define ZsensorLM75   "LM75"    //ESP8266, Arduino, ESP32
 //#define ZsensorDHT     "DHT"      //ESP8266, Arduino, ESP32,  Sonoff RF Bridge
 //#define ZsensorDS1820  "DS1820"   //ESP8266, Arduino, ESP32
 //#define ZsensorGPIOKeyCode "GPIOKeyCode" //ESP8266, Arduino, ESP32