Added pass-through to delegate of controller:didChangeSection:atIndex:forChangeType:

Without this change, if you have sections with rows in them, and delete the section (with a cascade delete in the data model), then the section gets deleted in the model, but since the delegate's controller:didChangeSection:atIndex:forChangeType: isn't being called (although controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: is called), nothing is ever calling deleteSections:withRowAnimation: and so an exception gets thrown during controllerDidChangeContent:, and the table isn't properly updated.