Add support for kns:/ urls to the knewstuff-dialog tool
This adds in support for the kns URLs used in e.g. kpackagetool to canonically reference a specific entry found on a knewstuff provider. The result is that by passing in such a URL to the knewstuff-dialog tool, we interpret this as wanting to show the details for that specific entry.
The origin of this functionality was a short discussion on plasma/discover!63 (merged) where the need for such functionality became obvious.