Add goodwe backend

[rlagerweij]

These commits make my setup at home work with Sunalyzer. I have an GoodweDNS 4200W solar inverter and a HomeWizard P1 Wifi reader for my smart meter. Since the solar production and grid consumption are registered by two separate devices, I took it upon myself to adapt the grabber for multiple devices. I've tried to split out the various changes that I made into as small as possible chuncks, but I have had to modify the Fronius and Dummy device classes as well.

I think none of the changes should affect existing installations but I obviously can't fully check that since I don't own a Fronius inverter.

[n9yty]

This is some nice work. It is a bit old and still sitting here? Why not merge this in? In my case where my Fronius unit doesn't have a smart meter, I could perhaps pull data from another source (I have an Emporia monitor system).

@BorisBrock I know this would likely have to be updated now after the other changes, but can this be re-evaluated? It would be nice to be able to bring in my Emporia usage monitoring data, but it would require the support of multiple devices as offered in this patch.

[n9yty]

I did revise a copy of this locally, but I see it might need some work. It is fixed to only five devices, that should probably be made more dynamic. Also, the new "specific_option", while unused, is defined for the device type not the individual devices. I do have this running here, and am looking at adding an Emporia device, but I can see why this may not be an ideal merge.