retrieveServiceMetadata

Fetch the service's GetCapabilities document once (trying WFS 2.0.0 then 1.1.0). Callers that issue many requests against one service — e.g. earth.worldwind.ogc.wfs.WfsTiledFeatureSource fetching per tile — should retrieve this ONCE and pass it as serviceMetadata to createLayer, so the (large) capabilities document isn't re-downloaded for every request (which can overwhelm a server into timing the capabilities request out). Null if neither version could be retrieved.