[change] new accessibility features and docs

* Change 'accessible' to align with React Native.
* Add support for 'importantForAccessibility'.
* Stop event propagation for keyboard-activated Touchables (nested
  Touchables now respond the same as when touch-activated).
* Fix whitespace layout of nested Text elements.
* Use 'div' for Text to improve TalkBack grouping.
* Rewrite accessibility docs.

Close #382
Fix #408

README.md

@@ -20,7 +20,7 @@ touch handling to the Web. [Read more](#why).
 
 Browse the UI Explorer to see React Native [examples running on
 Web](https://necolas.github.io/react-native-web/storybook/). Or try it out
-online with [React Native for Web: Playground](http://codepen.io/necolas/pen/PZzwBR).
+online with [React Native for Web: Playground](https://www.webpackbin.com/bins/-KgucwxRbn7HRU-V-3Bc).
 
 ## Quick start
 
@@ -144,7 +144,6 @@ AppRegistry.runApplication('MyApp', { rootTag: document.getElementById('react-ro
 * [react-native-web-player](https://github.com/dabbott/react-native-web-player)
 * [reactxp](https://github.com/microsoft/reactxp)
 * [react-web](https://github.com/taobaofed/react-web)
-* [rhinos-app](https://github.com/rhinos-app/rhinos-app-dev)
 
 ## License