Investigate if windmills can be solar rather than electric energy interface

[KiwiHawk]

WIndmills don't show any production information in their item tooltips as these can be adjusted at run time. With the new solar panel properties, investigate if windmills should internally become solar panels rather than electric energy interfaces.

2.0.48

• Added SolarPanelPrototype::performance_at_day, performance_at_night and solar_coefficient_property.

[KompetenzAirbag]

I tried that just now and it won't work because the SolarPanelPrototype doesn't implement a graphics_set for animations, only a static picture and overlay property.

[KiwiHawk]

Solar panels have stateless_visualisation which has animation.