Include required framework for ALAssetsLibrary-CustomPhotoAlbum

Hi,

I'm not even sure if the changes I propose are correct, I just tried to use this pod and found that I had to include the AssetsLibrary manually, googled a bit and found the "supposed" way to do it... sorry if it doesn't make sense.

Also, I guess that @Kjuly, the responsible for the source repository for this lib, may have something to say...