Update AFIncrementalStore to AFNetworking 2.0.0

This a next (hacky) version of @Nitewriter's https://github.com/AFNetworking/AFIncrementalStore/pull/242 that maps `AFRestClient` to `AFHTTPRequestOperationManager`.

I have only tested this with the 'Basic Example' so code reviews/tests are really appreciated.

Really want to know the actual port approach that the author wants to take. I suppose taking advantage of `NSURLSession` is really desired.