Adjustments menu: add "Auto" sub-menu

Ideally, I'd like the "auto" options to live right in the main
Adjustments menu.  But because I don't know how many will actually be
included, and it's a ton of work to shift all index values for the many
menus and submenus beneath it (especially in the menu icon and
accelerator functions), I'm starting with a sub-menu for now.

Current submenu is just placeholders; none do anything just yet.