Add overlays and Sheets-style dropdown menus

Menus open from the menu bar as boxes composited over the grid with
Lip Gloss layers, so the grid underneath never moves. Alt+F, Alt+E,
Alt+V, Alt+I, Alt+O, Alt+H (as in Sheets) or F10 open them; arrows move
and cross between menus, Right and Left open and close submenus, Enter
runs, Esc closes one level and a letter jumps to the items starting
with it. With the mouse, click a title to open it, hover to highlight
and to switch menus, click an item to run it and click elsewhere to
close. Each item shows its shortcut as a key chip; unavailable items are
dimmed and skipped, items whose command isn't registered are hidden,
and menus too tall for the screen scroll. The status line describes the
highlighted item.

Quitting with unsaved changes asks on the context line instead of in a
menu: Enter saves and quits, D discards, Esc cancels. Key hints now
show keys as chips too.

commit

f59a529b9025e20c88796cddd913f62404d25e6f

parent

71a8e6cb649f80b4d32a6a9bccc58bbfb6f07a7f

author

Dami <dami.etoile@gmail.com>