This works just like show-urls-launch, except that instead of opening
the URL (typically using xdg-open), it is placed in the clipboard when
activated.
While parenthesis and brackets _are_ valid URL characters, there are
many times when we do *not* want them to be part of the URL.
For example, in markdown we write “[text](url)”, or even
“[](url-2)”.
Here, the URLs are clearly *not* “url)” or “url-1)](url2)”.