This patch allows user to not only add a chapter track but also remove
the total track. This means that you can have only the total track or
only the chapter track.
This patch does not allow user to have no track at all. Disabling one
track will automatically enable the other one, if that one is already
disabled.
The reasoning behind this is that for long-ish audio books, users will
not very often look at the overall progress. In fact, I find the
progress bar mostly useful only for quickly seeking to a position when
jumping back a few seconds is not sufficient.
In the seldom occasion that I want the overall progress, I can easily
get it from the book details page.
