Port to iOS 7

I just finished porting CoreObject to iOS, all tests pass for both TestCoreObject (iOS) and TestCoreObject on my machine. BasicPersistence (iOS) runs without issues too. 

I'm using Xcode 6 beta 3 and running iOS targets inside the iPhone 5S simulator with iOS 8. This means the compatibility with Xcode 5 could require some adjustments.

I haven't ported the Benchmark target to iOS yet. I'll do it soon.