modify the UIImageView+AFNetworking category to support callback with image data

modify the UIImageView+AFNetworking category to support callback with image data

the origin implementation only provides image which is pre-handled. this image
shows only one frame even if it is a gif. adding the 'data' param can give developer
a chance to do what they want to with the raw binary data, maybe use OLImageView
to show gif.

also modified the cache to support caching data.