feat(Windows): Adds Windows support to react-native-video

This PR adds react-native-windows support to react-native-video.  The Video component is implemented with a XAML MediaPlayerElement.  Most of the features implemented by Android (and some additional ones) are implemented by Windows.

Known issues and missing features include:
* onReadyForDisplay event
* local URI convention (e.g., "broadchurch" in examples changed to require("./broadchurch.mp4")
* `playableDuration` in `onVideoProgress` event is always 0.0
* `playInBackground` is not yet supported
* Volume settings are applied, but the UWP control does not handle it properly

Video.js

@@ -125,7 +125,7 @@ export default class Video extends Component {
     }
 
     const isNetwork = !!(uri && uri.match(/^https?:/));
-    const isAsset = !!(uri && uri.match(/^(assets-library|file|content):/));
+    const isAsset = !!(uri && uri.match(/^(assets-library|file|content|ms-appx|ms-appdata):/));
 
     let nativeResizeMode;
     if (resizeMode === VideoResizeMode.stretch) {