fix(MessageHandler): suppress the notifications on top of the overlay

modules/UI/UI.js

 };
 
 /**
- * Indicates if the ring overlay is currently visible.
+ * Indicates if any the "top" overlays are currently visible. The check includes
+ * the call overlay, GUM permissions overlay and a page reload overlay.
  *
- * @returns {*|boolean} {true} if the ring overlay is visible, {false} otherwise
+ * @returns {*|boolean} {true} if the overlay is visible, {false} otherwise
  */
-UI.isRingOverlayVisible = function () {
-    return RingOverlay.isVisible();
+UI.isOverlayVisible = function () {
+    return RingOverlay.isVisible()
+        || PageReloadOverlay.isVisible()
+        || GumPermissionsOverlay.isVisible();
 };
 
 /**

modules/UI/gum_overlay/UserMediaPermissionsGuidanceOverlay.js

 }
 
 export default {
+    /**
+     * Checks whether the overlay is currently visible.
+     * @return {boolean} <tt>true</tt> if the overlay is visible
+     * or <tt>false</tt> otherwise.
+     */
+    isVisible () {
+        return $overlay && $overlay.parents('body').length > 0;
+    },
     /**
      * Shows browser-specific overlay with guidance how to proceed with
      * gUM prompt.
     show(browser) {
         !$overlay && buildOverlayHtml(browser);
 
-        !$overlay.parents('body').length && $overlay.appendTo('body');
+        !this.isVisible() && $overlay.appendTo('body');
     },
 
     /**

modules/UI/reload_overlay/PageReloadOverlay.js

 }
 
 export default {
+    /**
+     * Checks whether the page reload overlay has been displayed.
+     * @return {boolean} <tt>true</tt> if the page reload overlay is currently
+     * visible or <tt>false</tt> otherwise.
+     */
+    isVisible() {
+        return $overlay && $overlay.parents('body').length > 0;
+    },
     /**
      * Shows the page reload overlay which will do the conference reload after
      * the given amount of time.
 
         !$overlay && buildReloadOverlayHtml();
 
-        if (!$overlay.parents('body').length) {
+        if (!this.isVisible()) {
             $overlay.appendTo('body');
             start(timeoutSeconds);
         }

modules/UI/util/MessageHandler.js

                      messageArguments, options) {
 
         // If we're in ringing state we skip all toaster notifications.
-        if(!notificationsEnabled || APP.UI.isRingOverlayVisible())
+        if(!notificationsEnabled || APP.UI.isOverlayVisible())
             return;
 
         var displayNameSpan = '<span class="nickname" ';