Add one way to have different configs for different versions and both to Javascript and native code

[myrjola]

From http://rickyreusser.com/2016/05/14/things-i-learned-the-hard-way-using-react-native/

Android: https://gist.github.com/rreusser/77c18ca38a6848876c22a00d3fed99a9 iOS: https://gist.github.com/rreusser/283e032fb1bb5f59256fd5b96f8b8e6c