Multiple inverter support rollup

[WillCodeForCats]

This is my big merge with the version I'm running for my multiple inverter installation adding in all the battery/control stuff that happened in the interim.

This was developed on a system that consists of two inverters and one meter:

• Inverters (addressed 1 and 2) on bus RS485-1
• Ethernet connected to inverter 1 with modbus/tcp enabled
• E+I meter 1 (address 2) connected to inverter 1 on bus RS485-2.
• Ethernet is also for Solaredge comms - no wireless or cell options
• Both inverters are model SE7600H-US (setapp version)
• Meter is model SE-MTR240-NN-S-S1

This should also close out #12 and #47.

[WillCodeForCats]

It's night right now, so a bunch of data is just showing 0. I'll take this out of draft status when the sun comes up tomorrow and they go into production mode. Generally confident it will be good to go though.

[mpredfearn]

Hey @WillCodeForCats - nice :-) There's a lot of commits here, but only about 3 logical changes - the overall diffstat looks fine. Do you think the commits could be rebased and squashed?
The multiple inverter code looks functionally identical to what's in #47 - although you have the hardware to be able to test it :-)

[WillCodeForCats]

My experience with github is new enough that I don't know what rebasing is. Probably what's happening is I forked this, manually applied #12 to my fork, then kept up with changes until release 1.4.0. When I tried to merge the very first battery additions into my fork github gave me all this crap about having to manually fix it and I gave up. Fast forward to now, even more changes, didn't know what to do, but I had some free time so all I could think of to do was undo things until github would stop complaining about merge conflicts, merge, then put what I'm running back in.

If you want to pull #47 in instead of this because it's close enough, I'll just clear this. But I'd rather stick with my codebase for testing, I don't want to test something new because the reports of bad data problems makes me nervous enough when my data collection has been perfect with what I'm running. Again, my experience with Python isn't up to the level where I can look at something and say "yeah that's the same".

So, Ive done the best I can do with what I know at this point.