Add bindings for I18nManager

I think there's no bindings for React Native I18nManager [module](https://github.com/facebook/react-native/blob/f0fb228ec76ed49e6ed6d786d888e8113b8959a2/Libraries/Utilities/I18nManager.js). Github search of _I18nManager _ in this repository showed no result.

If someone could confirm that it is missing and that it should be added, I might do a pull request for its bindings.