Completed artist.getInfo / AppDelegate changed

also the keys, method declarations, method implementations and calls are now sorted according to the JSON response from the API. Keep it that way.
Handling nil values correctly for NSString return methods & correcting other methods that called these

The NSString return methods now really return an NSString

DO NOT call methods that return NSStrings and then do introspection, it really doesn't work now
item renamed to obj

More common in Objective-C
using instancetype for the sharedManager Singleton