* wl-demo.el: Rewrote to make it read a logo file at the run-time.

* wl-demo.el: Rewrote to make it read a logo file at the run-time.
(wl-demo-icon-name): Use Xmas logo at the end of the year.
(wl-demo-insert-image): New function.
(wl-demo-insert-text): New function.
(wl-demo-image-type-alist): Redefine as a function.
(wl-demo): Use `wl-demo-insert-image' and `wl-demo-insert-text'.
(wl-demo-with-temp-file-buffer): Removed.
(wl-logo-xpm): Removed.
(wl-logo-xbm): Removed.
(wl-logo-bitmap): Removed.