[Bug] Shelly Switch shows on when power is disconnected 
**Describe the bug**
I’m not sure if this can be considered a bug maybe more like a feature. Or I haven’t been able to do this correctly. Anyway my problem is that when the Shelly device is powered off from a switch (no current at all to the Shelly device, lead is closed) it still shows on in HomeKit as on and the last set dim option. And I can turn it off or on. This stays on for ever. 

**My setup**
I have a Shelly dimmer 2 that is connected with neutral after the lamp switch. This is beucase the led lamp do not draw over 10w which is a must if it should be used only with lead. And when someone turns off the lamp switch it also cuts all the power to the Shelly device. Hope someone can give me an configuration option in how to solve this! :)

**Environment:**
 - Shelly device(s): Shelly Dimmer 2
 - Plugin version: 0.15.7
 - Device running homebridge: Mac Catalina

Is it possible to have some kind of ping option. And if it doesn’t respond then set to off. Don’t know if Shelly respond to ping. This is new for me but a great device :)
