[UX] Allow bulk deleting menu links.

I would love to be able to mass-delete menu links. As it is now, you have to select the "delete" action for each link. This loads another page for confirmation purposes. That is so tedious,

In Drupal-land, https://www.drupal.org/project/menu_editor seems to allow that. For D8, there's also https://www.drupal.org/project/menu_delete:

(there's a request to add this to D9 core: https://www.drupal.org/project/drupal/issues/2772961)

https://www.drupal.org/project/delete_menu_options is another interesting module:

Provides extra options when deleting a menu item. You can choose to delete child menu items and decide if the linking nodes should be deleted as well.

~~PS: While at it, can we also move the confirmation form to a modal?~~ (moved to a separate issue: #769)