Improvements and fixes

The string analysis now runs by itself, once a week and every night through a plant's first 30 days.

• An alert for a device that stopped sending data now closes once the device is back.
• Expected values now come from a flat-mounted irradiation sensor where a plant has one, and per inverter orientation where a plant faces several directions.
• At plants with many strings, the string analysis again measures a full 30 days, so a string that sent nothing reads as having no data.