Allow fullscreen mode in onlyoffice

www/common/sframe-common-outer.js

@@ -37,6 +37,7 @@ define([
         var $i = $('<iframe>').attr('id', 'sbox-iframe').attr('src',
             ApiConfig.httpSafeOrigin + (pathname || window.location.pathname) + 'inner.html?' +
                 requireConfig.urlArgs + '#' + encodeURIComponent(JSON.stringify(req)));
+        $i.attr('allowfullscreen', 'true');
         $('iframe-placeholder').after($i).remove();
 
         // This is a cheap trick to avoid loading sframe-channel in parallel with the