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A new class is defined: Y.WeatherPanel which extends Y.Panel. Y.WeatherPanel will load weatherdata using QYL which is inserted inside the panel. We will use weatherpanel.readyPromise() to show the widget only when all the weatherdata is inserted.
The widget sets a class .yui3-itsaweatherpanel-loading to the boundingBox by default when created.
Y.Widget is responsible for this. This class will be removed once the widget is rendered. However, the YQL-data has still to be laoded,
so this behaviour will show an empty panel on the screen. The panel gets filled later on when YQL returns its data.
To prevent this flickr-behaviour, Y.WeatherPanel adds the class .extendloading to the boundingBox at initialization, which will
keep the panel hidden. As soon as all the data is inserted (readyPromise), this class is removed and the weatherpanel shows up.