Remove dead desktopmodel/widget code
DesktopDelegate: Use enum for _hitwhich
notes: Break over-long line
PageWidget: Update preview with current page on minor change

The current code will always revert to showing page 1 in the preview when
a stack changed, even when the change is only minor (such as changing the
currently-visible page). Instead, show the current change.

Before this, when you used the delegate page arrows to change from p2 to
p3, the preview would display p1 then p3, a noticeable glitch.
Filejpeg: Implement size() properly, and add comments
desk: Fix unused variable warning in findFile()
File: Use const QString, and add comments
Fix bug claiming pages that have already been mentioned

If we come across page 2 twice, we notice the second time that it already
exists. But that still means we can claim it.
Filejpeg: Implement unstackPages()
Filejpeg: Use copyOrMovePageFile() for common copy/move ops
Filejpeg: Implement stackStack()
Update notes
Avoid duplicate filenames when creating files with page suffixes
Filejpeg: Implement remove() properly

This now needs to remove all pages attacked to a JPEG stack.