(menu-bar-options-save): Replace `fringe-indicators'

(menu-bar-options-save): Replace `fringe-indicators'
with `indicate-empty-lines' and `indicate-buffer-boundaries'.
(menu-bar-showhide-fringe-menu): Add new item "Empty line indicators"
running new function `toggle-indicate-empty-lines'.
Rename "Customize" item to "Customize fringe".
Rename "Indicators" item to "Buffer boundaries" and change help echo.
(menu-bar-showhide-fringe-ind-menu): Change several help echos.
Add `menu-bar-showhide-fringe-ind-customize' as "Other (customize)".
Delete "Empty lines only" item.
(menu-bar-showhide-fringe-ind-customize): New function.
(menu-bar-showhide-fringe-ind-mixed)
(menu-bar-showhide-fringe-ind-box)
(menu-bar-showhide-fringe-ind-right)
(menu-bar-showhide-fringe-ind-left)
(menu-bar-showhide-fringe-ind-none): Use `indicate-buffer-boundaries'
instead of `fringe-indicators'.