HASS registration: use device_class instead of custom icon

function hass_register()

	local hass_device = string.format('{"connections":[["mac","%s"]],"identifiers":["%s"],"model":"ESP8266","name":"ESP8266 PM1006","manufacturer":"DIY"}', wifi.sta.getmac(), device_id)

	local hass_entity_base = string.format('"device":%s,"state_topic":"%s/data","expire_after":600', hass_device, mqtt_prefix)

	local hass_pm2_5 = string.format('{%s,"name":"PM2.5","object_id":"%s_pm2_5","unique_id":"%s_pm2_5","icon":"mdi:air-filter","unit_of_measurement":"µg/m³","value_template":"{{value_json.pm2_5_ugm3}}"}', hass_entity_base, device_id, device_id)

	local hass_rssi = string.format('{%s,"name":"RSSI","object_id":"%s_rssi","unique_id":"%s_rssi","icon":"mdi:wifi","unit_of_measurement":"dBm","value_template":"{{value_json.rssi_dbm}}","entity_category":"diagnostic"}', hass_entity_base, device_id, device_id)

	local hass_pm2_5 = string.format('{%s,"name":"PM2.5","object_id":"%s_pm2_5","unique_id":"%s_pm2_5","device_class":"pm25","unit_of_measurement":"µg/m³","value_template":"{{value_json.pm2_5_ugm3}}"}', hass_entity_base, device_id, device_id)

	local hass_rssi = string.format('{%s,"name":"RSSI","object_id":"%s_rssi","unique_id":"%s_rssi","device_class":"signal_strength","unit_of_measurement":"dBm","value_template":"{{value_json.rssi_dbm}}","entity_category":"diagnostic"}', hass_entity_base, device_id, device_id)

	mqttclient:publish("homeassistant/sensor/" .. device_id .. "/pm2_5/config", hass_pm2_5, 0, 1, function(client)

		mqttclient:publish("homeassistant/sensor/" .. device_id .. "/rssi/config", hass_rssi, 0, 1, function(client)