Display confirmation dialog before deleting slot

At the moment, as soon as user clicks x, application attempts to remove the slot from the key. If user is already authenticated as admin, there will be no prompt to confirm, user really wants the slot deleted. The app will go ahead and remove the key.

What we want instead is, when user clicks x:

1. Display a Yes/No dialog asking user to confirm, they really want to delete the slot.
2. If user clicks No, don't do anything. If they click Yes proceed with deletion.