Since all the listing tasks accepts an url as first argument (whatever the
argument name is), it makes sense to be able to create a new task withoutuse a simple common argument name for
having to dig in the code to remember what this url argument name is for this
specific listerthis. I've chosen 'url' instead of api_baseurl/forge_url/url.
Also kill now useless `new_lister()` functions.
Depends on D1949