Sensor device classes (#14282)

* Added light device class, moved device classes to const

* Removed unnecessary icons

* Replace 'lux' with 'lx'

* Fix comment

* Changed device_class name

homeassistant/components/sensor/mysensors.py

@@ -26,7 +26,7 @@ SENSORS = {
     'V_PERCENTAGE': ['%', 'mdi:percent'],
     'V_LEVEL': {
         'S_SOUND': ['dB', 'mdi:volume-high'], 'S_VIBRATION': ['Hz', None],
-        'S_LIGHT_LEVEL': ['lux', 'white-balance-sunny']},
+        'S_LIGHT_LEVEL': ['lx', 'white-balance-sunny']},
     'V_ORP': ['mV', None],
     'V_EC': ['μS/cm', None],
     'V_VAR': ['var', None],