Improved off-grid handling for solar only inverters

This changes the handling of solar inverters as some data loggers (T series) do not reliably go off-line when the inverter shuts down at sunset which can cause erroneous data in the sensors.

This corrects the behaviour by using the runningState flag which goes from 163 (on-grid) to 161 (waiting) when this happens and it will switch the internal state to off-line whilst the inverter is waiting for the next sun rise.