Issue/1861 upgrades afnetworking

- Updated the following Pods:
 - AFNetworking **Mk 2.3.1**
 - WordPress-iOS-Shared **Mk 0.0.3**
 - WordPressCom-Stats-iOS **Mk 0.0.3**
- Fixed code referencing to AFNetworkingErrorDomain string (that error domain got split into two)
- Nuked Pods from the User Header Search Paths. This was causing Xcode to pick up classess from 3rd party 'sample code'.
- Fixed a glitch in EditPostViewController

Thanks @astralbodies for helping me out!