image-dired: Show image info in header line

image-dired: Show image info in header line

* lisp/image-dired.el
(image-dired-update-header-line): New function to show image
information in the header line.
(image-dired-display-thumb-properties): Make obsolete.
(image-dired-track-thumbnail)
(image-dired--display-thumb-properties-fun)
(image-dired-forward-image, image-dired-next-line)
(image-dired-previous-line, image-dired-beginning-of-buffer)
(image-dired-end-of-buffer, image-dired-read-comment): Use
image-dired-update-header-line instead of
image-dired-display-thumb-properties.