关于UITabBar配置

为了适配6.0版本，需要做额外处理，同时由于7.0版本以后新增了一些API，如果没有注意到这些变化，

设置了图片并没有达到预期的效果。

下面是关键代码，适配了6.0：

  UITabBarItem *item2 = [[UITabBarItem alloc] init];
  item2.title = @"消息";
  if (kIOSVersion >= 7) {
    item2.image = [kImageWithName(@"messageUnselect") imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    item2.selectedImage = [kImageWithName(@"messageSelected") imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];

    [item2 setTitleTextAttributes:@{NSForegroundColorAttributeName : kAssistOrangeColor}
                         forState:UIControlStateSelected];
    [item2 setTitleTextAttributes:@{NSForegroundColorAttributeName : kBColor}
                         forState:UIControlStateNormal];
  } else {
    [item2 setFinishedSelectedImage:kImageWithName(@"messageSelected")
        withFinishedUnselectedImage:kImageWithName(@"messageUnselect")];

    [item2 setTitleTextAttributes:@{UITextAttributeTextColor : kAssistOrangeColor}
                         forState:UIControlStateSelected];
    [item2 setTitleTextAttributes:@{UITextAttributeTextColor : kBColor}
                         forState:UIControlStateNormal];
  }