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

windows/ReactNativeVideo/ReactVideoPackage.cs

@@ -0,0 +1,30 @@
+using ReactNative.Bridge;
+using ReactNative.Modules.Core;
+using ReactNative.UIManager;
+using System;
+using System.Collections.Generic;
+
+namespace ReactNativeVideo
+{
+    public class ReactVideoPackage : IReactPackage
+    {
+        public IReadOnlyList<Type> CreateJavaScriptModulesConfig()
+        {
+            return Array.Empty<Type>();
+        }
+
+        public IReadOnlyList<INativeModule> CreateNativeModules(ReactContext reactContext)
+        {
+            return Array.Empty<INativeModule>();
+
+        }
+
+        public IReadOnlyList<IViewManager> CreateViewManagers(ReactContext reactContext)
+        {
+            return new List<IViewManager>
+            {
+                new ReactVideoViewManager(),
+            };
+        }
+    }
+}