NET-37: convert from capturing kWhToday values to wattHourReading values. This way inverters that report accumulating values don't need to calculate them as an offset, while inverters that report daily offsets continue to work fine. SolarNet already expects a wattHourReading value, so no changes are needed on the server side.
Don't try to calculate E-Total as a daily offset. This is much more reliable (now supported from NET-37).
Update unit test to match latest code.