3-18-20: Added content uploading capabilities in Android and iOS SDKs

File upload capabilities have been added to iOS SDKs as well.

iOS Alamofire 5.x: https://github.com/pixlee/pixlee-ios-sdk/releases/tag/2.1.0
iOS Alamofire 4.9.x: https://github.com/pixlee/pixlee-ios-sdk/releases/tag/1.9.2
Android: https://github.com/pixlee/android-sdk/releases/tag/1.3.0