Undo support

[garrett]

Graphical file managers all have support for "undo", letting people undo actions, such as:

• delete
• move
• copy (it removes the copies)

These sometimes show up as toasts, such as:

(Not all file managers have toasts for this. GNOME Files does. But Dolphin, for example, does not. I haven't checked Explorer or Finder.)

But also are available with keyboard shortcuts "control-z" (or "command-z" on a Mac) and on context menus.