DZDocumentsPickerController 介绍
DZDocumentsPickerController 是一个文件导入工具，支持多种数据源的导入，包括 Image Library, iTunes
shared folder, and cloud services like Dropbox, Cloud App, iCloud, Google
Drive, Microsoft SkyDrive, SugarSync and Box.
DZDocumentsPickerController 官网
https://github.com/DZen-Interaktiv/DZDocumentsPickerController