Async and Configflow

[ad-ha]

Dears,

I've almost fully merged the code for a Async version and using Configflow. I just need to address an issue with the Next Invoice Amount sensor, which I've just submitted a Pull request for, and try to make it able to manage multi-contracts.

@bzzoiro and @tslpre, do you guys prefer me to get a full code pull request or how shall I make it?

In addition, does anyone with a gas contract can pull the data that the API response for the gas invoices and costs? I had it before, but right now I do not get the gas from Repsol anymore.

Cheers,