[VisionGlass] Create the GestureManager from an UI context

In order to initialize properly the GestureManager object it must be
created with an UI context, like for example an Activity. Use the Wolvic's
main activity to initialize it.

This was found by StrictMode. It was throwing the following exception:

Tried to access the API:GestureDetector#init which needs to have proper
configuration from a non-UI Context:com.igalia.wolvic.VRBrowserApplication@ff7c8aa
The API:GestureDetector#init needs a proper configuration. Use UI contexts such
as an activity or a context created via createWindowContext(Display, int, Bundle)
or  createConfigurationContext(Configuration) with a proper configuration.

java.lang.IllegalAccessException: Tried to access the API:GestureDetector#init which needs to have proper configuration from a non-UI Context:com.igalia.wolvic.VRBrowserApplication@ff7c8aa
      	at android.os.StrictMode.assertConfigurationContext(StrictMode.java:2297)
      	at android.view.GestureDetector.init(GestureDetector.java:480)
  	at android.view.GestureDetector.<init>(GestureDetector.java:440)
     	at android.view.GestureDetector.<init>(GestureDetector.java:408)
      	at com.igalia.wolvic.PlatformActivity$PlatformActivityPluginVisionGlass.setupPhoneUI(PlatformActivity.java:654)
   	at com.igalia.wolvic.PlatformActivity$PlatformActivityPluginVisionGlass.<init>(PlatformActivity.java:541)
   	at com.igalia.wolvic.PlatformActivity.createPlatformPlugin(PlatformActivity.java:531)
      	at com.igalia.wolvic.VRBrowserActivity.initializeWidgets(VRBrowserActivity.java:477)
       	at com.igalia.wolvic.VRBrowserActivity.onCreate(VRBrowserActivity.java:362)

app/src/visionglass/java/com/igalia/wolvic/PlatformActivity.java

@@ -527,16 +527,18 @@ private void initializeAGConnect() {
     }
 
     public final PlatformActivityPlugin createPlatformPlugin(WidgetManagerDelegate delegate) {
-        return new PlatformActivityPluginVisionGlass(delegate);
+        return new PlatformActivityPluginVisionGlass(delegate, this);
     }
 
     private class PlatformActivityPluginVisionGlass extends PlatformActivityPlugin {
-        private WidgetManagerDelegate mDelegate;
+        private final WidgetManagerDelegate mDelegate;
         private WMediaSession.Delegate mMediaSessionDelegate;
         private GestureDetector mGestureDetector;
+        private final Context mContext;
 
-        PlatformActivityPluginVisionGlass(WidgetManagerDelegate delegate) {
+        PlatformActivityPluginVisionGlass(WidgetManagerDelegate delegate, Context context) {
             mDelegate = delegate;
+            mContext = context;
             setupPhoneUI();
         }
 
@@ -650,7 +652,7 @@ public void onStopTrackingTouch(SeekBar seekBar) {
                 }
             });
 
-            mGestureDetector = new GestureDetector(getApplicationContext(), new GestureDetector.SimpleOnGestureListener() {
+            mGestureDetector = new GestureDetector(mContext, new GestureDetector.SimpleOnGestureListener() {
                 @Override
                 public boolean onScroll(@Nullable MotionEvent e1, @NonNull MotionEvent e2, float distanceX, float distanceY) {
                     // Use inverted axis so the scroll feels more natural.