Read actual turbulence value from "turbulence-magnitude-norm" property,
not from its "...-override" switch (which is true when enabled, so
turbulence was always forced to "1.0").
make options
--wind=nnn@mm
--visibility
--visibility-miles
--ceiling
--turbulence
work again. These options now write properties in the
/environment/config/presets
branch. The values will be applied in the property-rules
in FGDATA/Environment/interpolator.xml
Corresponds to commit e86cecf4704a4bdcf43114245d8ac94adb1f1eef
in fg/next
