Improve user feedback on source addition
When submitting source(s), nothing says that it has worked or not. Sometimes some bad sources are simply ignored but nothing tells that to the user (the new source "azerty" will simply be ignored). When an error occurs on a given URL, it fails at that one, URL before have been added but the following ones are not.
It would be useful to get return something like a map of URL and status (added, ignored, failed for instance) and printing that info to the user.