Long actions, such as file opening, playlist loading, metadata loading
and refreshing, etc, are now handled through NSProgress. Additionally,
a new status bar change displays the progress of the task instead of
the total duration of the playlist. Finally, app quit is blocked by a
running task, and if the app is quit while a task is running, it will
be delayed until the task completes, at which time the app will
terminate cleanly.
Signed-off-by: Christopher Snowhill <kode54@gmail.com>