Display 'Capture events' table in the Payment show page

The payment show pages should be able to display all the capture events for that payment. For that purpose there is a new partial that displays a table for all of the payments' capture events. The table will not be displayed if there are no captures for that specific payment.

The payment capture events are represented by the model `Spree::PaymentCaptureEvent`. In order to display a properly formatted amount for the event captures, the method `#display_amount` (using `Spree::Money`) was added to that model.