Improvements and fixes

The on-site analysis now reports strings missing from a plant. Strings now get results on days with late or partial readings.

• The on-site analysis now reports inverters taking in more DC power than their listed strings account for, and roughly how many strings are missing.
• Strings on a day whose data starts late now get a performance ratio, counted only over the hours with readings.
• Strings now get a panel count on days with readings only around midday, as the brightest readings now count too.
• The panel count entered for a string no longer overwrites the one the analysis measured, and both are kept.