Multiple bug fixes

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

The following are the files that have been fixed in this update.
【Fixed files】
admin/css/editor-style.css
admin/js/my_script.js
comments.php
functions.php
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