SHT3x driver

SHT3x driver, clean code
changes leading to merge TFHT with CUAV hygrometer
Delete humidity_temperature.msg
Update CMakeLists.txt
rename 'atmosphefir_quantities' to 'hygrometers'
fix logging
removed cmake files
fix PR issues

ROMFS/px4fmu_common/init.d/rc.sensors

@@ -130,6 +130,15 @@ then
 	fi
 fi
 
+# SHT3x temperature and hygrometer sensor, external I2C
+if param compare -s SENS_EN_SHT3X 1
+then
+	if ! sht3x start -X
+	then
+		sht3x start -X -a 0x45
+	fi
+fi
+
 # TE MS4525 differential pressure sensor external I2C
 if param compare -s SENS_EN_MS4525 1
 then