* adjusted to new requestWeatherGrid
* use fetchNextWeatherDataDeferred to make sure follow up calls are decoupled
* for callbacks use weatherRequest.callback.singleShot so it is called in correct thread
Instead of the existing one, this newly added API allows to request
a weather grid without a callback as argument. Instead the final grid
will be emitted as signal.
This API is also made available in ISimulatorContext for GUI access.
refs #663