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

example/windows/VideoPlayer/MainPage.cs

@@ -0,0 +1,55 @@
+using ReactNative;
+using ReactNative.Modules.Core;
+using ReactNative.Shell;
+using ReactNativeVideo;
+using System.Collections.Generic;
+using Windows.UI.Xaml.Media.Imaging;
+
+namespace VideoPlayer
+{
+    class MainPage : ReactPage
+    {
+        public override string MainComponentName
+        {
+            get
+            {
+                return "VideoPlayer";
+            }
+        }
+
+#if BUNDLE
+        public override string JavaScriptBundleFile
+        {
+            get
+            {
+                return "ms-appx:///ReactAssets/index.windows.bundle";
+            }
+        }
+#endif
+
+        public override List<IReactPackage> Packages
+        {
+            get
+            {
+                return new List<IReactPackage>
+                {
+                    new MainReactPackage(),
+                    new ReactVideoPackage(),
+                };
+            }
+        }
+
+        public override bool UseDeveloperSupport
+        {
+            get
+            {
+#if !BUNDLE || DEBUG
+                return true;
+#else
+                return false;
+#endif
+            }
+        }
+    }
+
+}