Cleanup/unmount notification overlay. (#705)

android/app/src/main/java/com/reactnativenavigation/layouts/BottomTabsLayout.java

         if (sideMenu != null) {
             sideMenu.destroy();
         }
+        slidingOverlaysQueue.destroy();
     }
 
     @Override

android/app/src/main/java/com/reactnativenavigation/layouts/SingleScreenLayout.java

         if (sideMenu != null) {
             sideMenu.destroy();
         }
+        slidingOverlaysQueue.destroy();
     }
 
     @Override

android/app/src/main/java/com/reactnativenavigation/views/slidingOverlay/SlidingOverlay.java

         Hidden, AnimateHide, Shown, AnimateShow
     }
 
-    private final ContentView view;
+    private ContentView view = null;
     private final RelativeLayout parent;
     private final SlidingOverlayParams params;
 
     public SlidingOverlay(RelativeLayout parent, SlidingOverlayParams params) {
         this.parent = parent;
         this.params = params;
-        view = createSlidingOverlayView(params);
     }
 
     public void setSlidingListener(SlidingListener listener) {
     }
 
     public void show() {
+        view = createSlidingOverlayView(params);
         parent.addView(view);
 
         final PeekingAnimator animator = new PeekingAnimator(view, params.position, true);
         animator.animate();
     }
 
+    public void destroy() {
+        visibilityState = VisibilityState.Hidden;
+        view.unmountReactView();
+        parent.removeView(view);
+    }
+
     public boolean isShowing() {
         return VisibilityState.AnimateShow == visibilityState;
     }
     }
 
     protected void onSlidingOverlayEnd(ContentView view) {
-        visibilityState = VisibilityState.Hidden;
-        view.unmountReactView();
-        parent.removeView(view);
+        destroy();
 
         if (listener != null) {
             listener.onSlidingOverlayGone();

android/app/src/main/java/com/reactnativenavigation/views/slidingOverlay/SlidingOverlaysQueue.java

                     pendingHide = true;
                 }
                 else if (currentOverlay.isVisible()) {
-                    if (autoDismissTimer != null) {
-                        autoDismissTimer.cancel();
-                        autoDismissTimer = null;
-                    }
+                    cancelTimer();
                     currentOverlay.hide();
                 }
             }
         dispatchNextSlidingOverlay();
     }
 
+    public void destroy() {
+        SlidingOverlay currentOverlay = queue.poll();
+        while (!queue.isEmpty()) {
+            queue.poll();
+        }
+
+        if (currentOverlay != null) {
+            cancelTimer();
+            currentOverlay.setSlidingListener(null);
+            currentOverlay.destroy();
+        }
+    }
+
     protected void dispatchNextSlidingOverlay() {
         NavigationApplication.instance.runOnMainThread(new Runnable() {
             @Override
             }
         });
     }
+
+    protected void cancelTimer() {
+        if (autoDismissTimer != null) {
+            autoDismissTimer.cancel();
+            autoDismissTimer = null;
+        }
+    }
 }