Multiple bug fixes

【Contents of fixes】
■Support WP5.6 (compatible with jQuery version upgrade)
■【Mac] Fixed a bug that Japanese and European characters may be displayed with different thickness when using some fonts.
■【macOS Big Sur】Fixed a bug that the YouTube video in the top page header content would not play in Chrome browser.

The following are the files that have been fixed in this update.
【Fixed files】
comments.php
editor-style-02.css
functions/head.php
functions/ogp.php
js/jquery.mb.YTPlayer.min.css
js/jquery.mb.YTPlayer.min.js
pagebuilder/assets/css/pagebuilder.css
style.css

【Added files】
js/jquery.easing.1.4.js