Make image-dired-display-image-mode inherit from image-mode

Make image-dired-display-image-mode inherit from image-mode

* lisp/image-dired.el (image-dired-display-image-mode):
Inherit from 'image-mode'.  (Bug#10758)
(image-dired-display-image): Don't generate a temporary image, which
is no longer needed with the above change.
(image-dired-display-thumbnail-original-image)
(image-dired-dired-display-image)
(image-dired-mouse-display-image): Simplify.

(image-dired-temp-image-file)
(image-dired-cmd-create-temp-image-program)
(image-dired-cmd-create-temp-image-options)
(image-dired-display-window-width-correction)
(image-dired-display-window-height-correction)
(image-dired-display-window-width)
(image-dired-display-window-height)
(image-dired-display-current-image-full)
(image-dired-display-current-image-sized)
(image-dired-window-height-pixels): Make obsolete.
(image-dired-create-display-image-buffer): Make into obsolete
function alias for 'ignore'.
(image-dired-display-image-mode-map): Simplify by removing things
duplicated from `image-mode-map'.  Disable some commands from
`image-mode-map' that doesn't make sense for Image-Dired.
(image-dired-display-image-mode-menu): Remove menu, as it no longer
contains anything useful.
(image-dired-minor-mode):
* doc/emacs/dired.texi (Image-Dired): Update documentation for the
above change.