Add support for Keyboard native module

[kmelmon]

Proposal: Add support for Keyboard module

Summary

This issue is tracking implementing the Keyboard native module in vnext. See https://facebook.github.io/react-native/docs/keyboard

Motivation

Basic example

Open Questions

[chrisglein]

Hey @ddalp, this one needs someone to dig in and find what's missing/broken. Can you give this one a breakdown?

[ddalp]

There are six types of events defined for keyBoard by React Native:
keyboardWillShow
keyboardDidShow
keyboardWillHide
keyboardDidHide
keyboardWillChangeFrame
keyboardDidChangeFrame

I think we can only map keyboardDidShow and keyboardDidShow for Windows.

[ddalp]

Checked in, we are now firing keyboardDidShow and keyboardDidHide events and verified keyboardAvoidingView works ok with the change.