Layout changes for iPad only.

The detail view is now shown modally in a form.
Used completion block to dismiss the modal detail view.

We changed the modal detail view controller to a form, so the item view is never hidden. Since it isn't hidden, the viewDidLoad/viewDidUnload methods aren't triggered, which reload the table data. We created a completion block to do so, passed it to the detail view, and updated the save: and cancel: methods to execute the completion block upon dismissal of the view controller.
BNRImage store is now thread-safe.