campaign deletion should have better warning message

[jshslsky]

In order to prevent admins or supervisors from accidentally deleting campaigns that have survey responses, we need to show a dialog that says "Hey, you are about to delete a campaign with X responses. This is a permanent action and the campaign and its responses will be gone forever. Are you sure you want to delete this campaign?" The text doesn't have to be this exact wording, but it should be very explicit that this is a destructive action.