Minor fixes: battery reporting and start time

We've released a minor update to the DOC AI Cam today. This includes

• a fix to improve the accuracy of the battery percentage calculation, and
• a fix to when the camera starts recording in high power mode with the default recording window (it was starting half an hour after sunset, rather than half an hour before)

There is also some functionality to run the AI in low power mode. This happens in the morning and at the moment can only be used by those cameras doing low bandwidth monitoring via the Celium network.