Improvements and fixes

Your string and combiner-box power now comes from the data logger, and a meter reporting zero lifetime energy no longer drags down your plant total.

• Where the logger reports no power for them, the figure is still worked out from voltage and current.
• You no longer see implausible spikes: over 15 kW or 40 A on a string, or over 250 A on a combiner box.
• A meter or inverter reporting a lifetime energy total of zero no longer drags your plant's energy total down with it.