* Systems/icing.xml: new.
Windshield temperature is the same as outside air temperature plus 18K
if windshield bleed air is "LOW" and plus 60 K if "HIGH". Bleed air
requires electrical power on the main_left bus and at least one running
engine.
Window icing occurs within 100 seconds if windshield temperature drops
below 0°C and relative humidity is high.
* Citation-II-common.xml: load it as a new property-rule.
* Models/Instruments/electricpanel.xml: add rotate and pick animations
and a tooltip to the "W/S BLEED AIR" switch.
