Add keyword :vert-only for tool bar items with labels not shown horizontally.

Add keyword :vert-only for tool bar items with labels not shown horizontally.

* lisp/info.el (info-tool-bar-map): Add some :vert-only keywords.

* lisp/tool-bar.el (tool-bar-setup): Add some :vert-only keywords.

* src/dispextern.h (tool_bar_item_idx): Add TOOL_BAR_ITEM_VERT_ONLY.

* src/gtkutil.c (xg_make_tool_item): Take vert_only as argument.
Set important to ! vert_only.
(xg_show_toolbar_item): Don't show label horizontally if
tool item isn't important.
(update_frame_tool_bar): Get TOOL_BAR_ITEM_VERT_ONLY and pass it to
xg_make_tool_item, or update important on existing tool item.

* src/keyboard.c (QCvert_only): New variable.
(parse_tool_bar_item): Check for QCvert_only.
(syms_of_keyboard): Initialize QCvert_only.