LTR/RTL directionality suport

Add dir-ltr|rtl to h5p-content div, based on iframe parent document directionality.
(Which will help us address proper rtl alignment and directionality css selectors, in future patches)

Fix is only needed for iframe embedding. as parent document directionality is already available to div embedding.

js/h5p.js

@@ -111,6 +111,9 @@ H5P.init = function (target) {
       params: JSON.parse(contentData.jsonContent)
     };
 
+    // Add dir-ltr|rtl to h5p-content div, based on iframe parent document directionality.
+    $element.addClass('dir-' + window.parent.document.dir);
+
     H5P.getUserData(contentId, 'state', function (err, previousState) {
       if (previousState) {
         library.userDatas = {