Function append_favorite_button 

fn append_favorite_button(
    menu: &Menu,
    ui: &Rc<LibraryWindowUi>,
    item: &AssetObject,
    hooks: &AssetMenuHooks,
)

“Add to / Remove from Favorites”. The opening view is told through on_edited so a lightbox can refresh its heart, and through on_trashed when the Favorites view drops it.