open(1) was able to handle most URLs as well as paths, but not file://
URLs (which occur when dragging something from the output of ls, for
example). We have to create an URL from the user-supplied argument using
create_with_url_or_path(), check whether it's a file:// URL or not and
*then* use real_path_for() on the URL's path().
Moves DirectoryServices out of LibCore (because we need to link with
LibIPC), renames it Desktop::Launcher (because Desktop::DesktopServices
doesn't scan right) and ports it to use the LaunchServer which is now
responsible for starting programs for a file.
