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/config_LM75.h

@@ -0,0 +1,58 @@
+/*
+  OpenMQTTGateway Addon  - ESP8266 or Arduino program for home automation
+
+   Act as a wifi or ethernet gateway between your 433mhz/infrared IR signal  and a MQTT broker
+   Send and receiving command by MQTT
+
+   This is a Temperature Addon:
+   - Measures Temperature
+   - Generates Values for: Temperature in degrees C and F
+   - Required Hardware Module: LM75 or NCT75
+   - Required Library: jeremycole/I2C Temperature Sensors derived from the LM75
+
+   Connection Schemata:
+   --------------------
+
+   LM75 ------> Arduino Uno ----------> ESP8266
+   ==============================================
+   Vcc ---------> 5V -------------------> Vu (5V)
+   GND ---------> GND ------------------> GND
+   SCL ---------> Pin A5 ---------------> D1
+   SDA ---------> Pin A4 ---------------> D2
+
+    This file is part of OpenMQTTGateway.
+
+    OpenMQTTGateway is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenMQTTGateway is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef config_LM75_h
+#define config_LM75_h
+
+extern void setupLM75();
+extern void LM75toMQTT();
+
+#define lm75_always            true // if false when the current value of the parameter is the same as previous one don't send it by MQTT
+#define TimeBetweenReadinglm75 30000
+
+/*----------------------------USER PARAMETERS-----------------------------*/
+/*-------------DEFINE YOUR MQTT PARAMETERS BELOW----------------*/
+#define LM75TOPIC "/TEMPtoMQTT/lm75"
+
+#if defined(ESP32)
+#  if !defined(I2C_SDA) || !defined(I2C_SCL)
+#    define I2C_SDA 16
+#    define I2C_SCL 0
+#  endif
+#endif
+
+#endif