The automatic runway selection code in startup.nas depends
on a valid metar before /sim/signals/nasal-dir-initialized
is fired. If the METAR arrives after that signal, no automatic
runway selection is performed. This patch waits for a METAR
on the first update() loop of the subsystem.
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