New feature that allows to limit the max power from the Grid

[RichieB2B]

This is a simple rebase of #220

Enable this new feature through policy configuration in the config.json file.

[RichieB2B]

I have improved the load balancing by introducing the getConsumptionAmps() method for EMS modules. When an EMS module is capable of returning the actual amount of Amps being used it can now do so. The limiter will then use this instead of guesstimating it using self.convertWattsToAmps().

I have written a new EMS modules for the P1 port of smart meters in #509 that has getConsumptionAmps() support.

This works quite well as you can see in the screenshot below. When a single phase goes above maxAmpsAllowedFromGrid (25A in my case) the TWC is scaled back immediately. The algorithm is quite aggressive and results in under utilisation for a minute. I don't mind this because it is an error on the side of caution.

[RichieB2B]

I have been using this code for 3 months now and it is very stable. It is ready to be merged.