World Outline feeds support cloud element

I want realtime updates from my world outline feed.

There's a new table of prefs on the workstation at user.opmlEditor.worldOutline.prefs.cloud.

After the feed is saved on the server, he pings using the coordinates in the cloud element. Assuming that the server supports the same XML-RPC ping handler we support in rssCloud.root. If not, well there will be a problem. (Realtime updates won't work, which is why we always fallback to polling.)

Actually it wouldn't be so hard to work around. We also support HTTP-POST on our server, and if that's what the cloud element calls for we could just use that. But for now the XML-RPC approach is sufficient.

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