Classes created with this mixin remember their keybindings so the keybindings
can be removed and then restored.
Sets the keyboard shortcut to the setting it had when the class was
created.
These menus can save and restore the underscores (indicated via the
& characters in the original labels) in their labels.
If the preference
'framework:menu-bindings is
#f, calls
erase-underscores during
initialization.
Erases the underscores in the label of this menu, but remembers them so
they can be restores with
restore-underscores.
Restores underscores in the menu’s label to their original state.