Fix and improve UI of scroll bar menu (bug#27047)

Fix and improve UI of scroll bar menu (bug#27047)

In addition, since the Emacs manual writes "scroll bar", "tool
bar" and "menu bar", use this convention in the Show/Hide menues
and tooltips as well.

* lisp/menu-bar.el (menu-bar-showhide-scroll-bar-menu): Make
pressing a radio button in the menu actually show that it was
pressed.  Replace the two radio buttons to turn the horizontal
scroll bar on and off with a single check-box toggle and add a
separator between this and the vertical scroll bar radio
buttons.  Use conventional spelling.
(menu-bar-horizontal-scroll-bar)
(menu-bar-no-horizontal-scroll-bar): Remove, since now unused.
(menu-bar-showhide-tool-bar-menu, menu-bar-showhide-menu)
(menu-bar-mode): Use conventional spelling.