Adapt Electric Buffer Menu to recent Buffer Menu changes.

Adapt Electric Buffer Menu to recent Buffer Menu changes.

* lisp/ebuff-menu.el (electric-buffer-list): Put electric buffer menu
command descriptions in this docstring, instead of the docstring
of electric-buffer-menu-mode.  Code cleanups.
(electric-buffer-menu-mode): Use define-derived-mode.  Rename from
Electric-buffer-menu-mode.
(electric-buffer-update-highlight): Minor code cleanup.

* lisp/emacs-lisp/tabulated-list.el (tabulated-list-format)
(tabulated-list-entries, tabulated-list-padding)
(tabulated-list-sort-key): Make permanent-local.