Make iOS SDK V2 available as a CocoaPod

I've modified the SDK a tad to make it ready to be a CocoaPod and have included the spec I used locally to get it working. With some minor tweaks, you can release this as an official CocoaPod. I removed pulling down the custom BoxODRefreshControl and am using a reference to the original podspec. I did NOT do the same for the BoxISO8601DateFormatter since I couldn't quickly find a podspec for it though I updated it to ARC.

Feel free to contact me if you need more information.