尝试实现取消及添加新player功能

这里有bug：

- (void)playerDetailsViewController:(PlayerDetailsViewController
*)controller didAddPlayer:(Player *)player
{
    [self.players addObject:player];
    NSIndexPath *indexPath = [NSIndexPath
indexPathForRow:([self.players count] - 1) inSection:0];
    [self.tableView insertRowsAtIndexPaths:@[indexPath]
withRowAnimation:UITableViewRowAnimationAutomatic];
    [self dismissViewControllerAnimated:YES completion:nil];
}