给视图添加倒影效果（包括图片视图）

原理剖析：
    在视图中的主图层（CALayer）再添加一个子图层，确定其frame（位置），copy一份主图层的内容然后绕Y轴翻转一下---   
const CGFloat kReflectPercent = 0.25f;
    const CGFloat kReflectOpacity = 0.7f;
    const CGFloat kReflectDistance = 5.0f;
    
    CALayer *reflectionLayer = [CALayer layer];
    reflectionLayer.contents = [self.image layer].contents;
    reflectionLayer.opacity = kReflectOpacity;
    reflectionLayer.frame = CGRectMake(0.0f,self.image.frame.size.height+kReflectDistance,self.image.frame.size.width,self.image.frame.size.height*kReflectPercent);  //倒影层框架设置，其中高度是原视图的百分比
    
    CATransform3D stransform = CATransform3DMakeScale(1.0f,-1.0f,1.0f);
    //CATransform3D transform = CATransform3DTranslate(stransform,0.0f,0.0f,0.0f);
    reflectionLayer.transform = stransform;
    reflectionLayer.sublayerTransform = reflectionLayer.transform;
    [[self.image layer] addSublayer:reflectionLayer];