Loop playback problems

The changes in the way the loop playback cursors are managed introduced problems with the loop playback feature :

#1 : If we open a score and immediately clic the Loop playback button, no In/Out cursors appears. So if we clic the start button, no sound is been played.

#2 : A full score playback isn't possible because now we can't set the Out position of the loop if we select the last note of a score. This makes also loop playback on Select All (Crtl+A) impossible.

#3 : There's also a problem with the cursor on a multi instruments score. If we drag a staff to increase space between the staffs, the cursor size doesn't change.

#4 : The loop cursors positions aren't updated if we change the view to Continuous view.