Long Down command for security reasons

[guillebot]

I'm stress testing this and it can happen under some conditions that the stored percentaje doesn't match with the real position.

I know that I can trigger a recalibration (assuming that I use the current sensor), but I would like a lot to have a "long down reset to closed" command. That I could send in an uncertain event, perhaps away from home or with power supply problems (very common in Argentina), to ensure that everything it's closed down and safe.

Should you want it I can work on it and submit a pull request.

Thanks