Remove animation when upload gif image

上传带动画的gif时候，如果在carrierwave中有resize会报错
添加一个progress，上传gif的时候去除动画
参考于[Carrierwave + MiniMagick - How to squash animated GIFs to their first frame?](http://stackoverflow.com/questions/13480499/carrierwave-minimagick-how-to-squash-animated-gifs-to-their-first-frame)