iOS SDK Improvements

I've updated the iOS SDK to use AFNetworking 2.X. This allows us to use WIT with modern apps that use the new version of the framework. It means dropping iOS 5 support, but even Apple doesn't include that in Xcode these days.

I've also made a few tweaks to how the recorder behaves (super short recordings are not uploaded, failedRecording sound can be played if recording fails or is too short). The recorder also uses didFinishPlaying to unlock noise state, because using a GCD timer based solution could become out of sync on heavy device load.

A few 64 bit compiler warnings have also been squelched.