Summary:
change `setTextAlign` and `setTextAlignVertical` to receive argument of type `String` (the same as in `StyleSheet`), so that native props and stylesheet props are calling the same ReactMethod
- add demo (may not be necessary)
Closes https://github.com/facebook/react-native/pull/4481
Reviewed By: svcscm
Differential Revision: D2823456
Pulled By: mkonicek
fb-gh-sync-id: 349d17549f419b5bdc001d70b583423ade06bfe8