Show matcher should be scoped to the expected object

Right now, the show matcher ignores what is passed to expect. It just looks to see if the specified page object is anywhere on the page. When we expect one page object to be a child of another, it would be nice to be able to say something like

expect(dashboard).to show :deed_form

This example comes from user_logs_deed_spec.rb. Right now, we can only assert that both objects are on the page:

expect(page).to show :deed_form
expect(page).to show :dashboard

With the way things are now if we were to say expect(dashboard).to show :deed_form it would pass, even if the deed form wasn't a child of the dashboard but was elsewhere on the page.