Improvements and fixes

The plant analysis no longer writes off strings or inverters on the strength of a day when the plant was dark or partly out.

• Strings are no longer marked as not connected after a day the plant was dark or hardly reporting.
• A string marked that way earlier clears itself once it measures again, instead of waiting to be cleared by hand.
• An inverter that was out for part of the day is no longer reported as producing far below what is expected of it.
• An event closed on an inverter no longer re-opens by itself on a day that inverter recovered.
• Configured strings that have never produced now count in the expected values and can raise events.
• An alert about a data source that came back while the on-site agent restarted no longer stays open.