Fixed multiple bugs

【Contents of the fix】
■【macOS Big Sur】Fixed an issue where the YouTube video in the top page header content would not play in the Chrome browser.
■Adjusted the style of iframe tags.
■Page builder update (compatible with WordPress 5.5)

The following are the files that have been modified for this update.
【Fixed files】
functions/update_notifier.php
js/jquery.mb.YTPlayer.min.css
js/jquery.mb.YTPlayer.min.js
languages/ja.mo
languages/ja.po
pagebuilder/assets/admin/css/admin.css
pagebuilder/assets/admin/js/admin.js
pagebuilder/assets/admin/js/editor.js
pagebuilder/assets/admin/js/repeater.js
pagebuilder/assets/admin/js/slider.js
pagebuilder/modules/googlemap.php
pagebuilder/modules/slider.php
pagebuilder/modules/tab.php
pagebuilder/pagebuilder.php
style.css