Add UIAccessibility to showImage:status:duration:

Follow up to @julienp's excellent pull request #101 by adding voice over to `showImage:status:duration:`, mostly so status is spoken when showing success/error HUDs afterwards incase someone needs to know whether their request failed or so on.

The status will cut out if it's too long, but considering the success/error HUDs are only displayed a short time anyway should be keeping the message short anyway. Could listen for `UIAccessibilityAnnouncementDidFinishNotification` and then start the fade out timer, which I can add if needed.