Set article's relative URLs to absolute after copy

[csarven]

On Save As with copy to storage selection generally two things happen: article's relative references are updated, and the relative resources are copied to destination using the same structure at source.

At the moment, there is an assumption that the copy operation succeeds and resulting location of the resources is what was initially requested. It is possible that the server may not agree with the PUT or POST location, hence the URLs in the article (the ones being changed from relative to absolute) should reflect the actual locations.

Suggested solution: first copy the resources, and then update the references based on response's Location header.