Most of the time, only the titles need to be updated, the track numbers
don't change. Yet, the first time, they both need to be set, so it is
easier to have a single command. Setting the track numbers along with
the titles, when not necessary, is not too much annoying. With a single
command, we make sure that everything is up to date, and in sync with
the filenames.

Signed-off-by: Cédric Marie <cedric@hjuvi.lautre.net>