This is the initial commit for a reworked environment controller.
The main intention is to decouple the individual modules like
metar fetch, metar properties, environment interpolation etc.
to make it easier for other weather module developers to modify
environment settings.
As a side effect, the dialogs for weather-scenario, weather-conditions,
clouds and precipitations have been merged into a single dialog
Square the normalized direction acceleration for the y and z axes, so
that turbulence predominantly affects pitch.
Bind to the /environment/turbulence/magnitude-norm and
/environment/turbulence/rate-hz properties in FlightGear.
