add delete confirmation to task on paper manage page

— RW + DT
as a matter of course I'll point out that you should be careful making any assertion based on the result of an `all()` in our specs, since `all` is synchronous.  I don't think the `expect {}` block will protect you either.  the `click` method doesn't intrinsically know what its side effects should be.  you might want to forgo the change stuff and do a `expect(page).to have_css('.card', count: (old_count - 1))` or something to that general effect.  Every time I've asserted based on `all` it's led to me having to find an intermittent spec on ci later.