mapfishapp: KML file upload: unsupported ExtendedData

test file: https://github.com/georchestra/georchestra/blob/master/mapfishapp/src/test/resources/org/georchestra/mapfishapp/ws/upload/kml_4326_accidents.kml

Only "visibility" and "open" attributes are returned in the GeoJSON, when we rather expect id, date, meteo ...

This is for @mpazos ;-)

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