ref(filmstrip): add class to body for horizontal filmstrip

modules/UI/UI.js

         SidePanels.init(eventEmitter);
     }
 
-    interfaceConfig.VERTICAL_FILMSTRIP
-        && $('body').addClass('vertical-filmstrip');
+    const filmstripTypeClassname = interfaceConfig.VERTICAL_FILMSTRIP
+        ? 'vertical-filmstrip' : 'horizontal-filmstrip';
+
+    $('body').addClass(filmstripTypeClassname);
 
     document.title = interfaceConfig.APP_NAME;
 };