Make it possible to run the same test against multiple URIs

[theseion]

We sometimes need to duplicate tests in order to run the same test against multiple URIs (especially in rule exclusion tests). It would be great if we could simply specify a list of URIs and reuse the test data for each of them. I think we could add a new field called uris that takes a list, so we'd have both uri (single URI, backwards compatibility) and uris (multiple URIs).