AFNetworking 2.0

This upgrades AFNetworking to 2.0, which was needed for me because I'm relying on AFNetworking 2.0. AFNetworking 2.0 isn't backwards compatible with the 1.0 branch. 99% of the changes in this PR are from AFNetworking itself from the Pods dir which are checked in. My changes are isolated to DZNPhotoServiceClient.