IxoDataSource: Refactor and add synchronous ranged download support.

- Use AFNetworking for all HTTP requests.
- Remove abuse of -initWithContentsOfURL in -downloadDataFromURL.
- Tweak IxoDownloadOperation to support omission of listener.
- Add -downloadFromURL:withRange to IxoDataSource.
- Add test for synchronous ranged requests.

Change-Id: I33a083b22c42cf034e48867a99e042c3358c7f11
4 files changed