Added functions/updated page builder

【Contents of modification】
■Added “Custom CSS”, “Custom Script”, and “SEO Settings (meta tags)” functions to the individual page editing screens (posts, custom posts, and fixed pages).
■Page builder update (compatible with WordPress 5.5)

The following are the files that have been modified for this update.
【Modified file】
admin/inc/basic.php
functions/custom_script.php
functions/head.php
functions/update_notifier.php
js/slick.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/googlemap.js
pagebuilder/assets/admin/js/repeater.js
pagebuilder/assets/admin/js/slider.js
pagebuilder/assets/css/googlemap.css
pagebuilder/assets/css/pagebuilder.css
pagebuilder/modules/catchcopy.php
pagebuilder/modules/googlemap.php
ddpagebuilder/modules/headline.php
pagebuilder/modules/image.php
pagebuilder/modules/includes/slick.php
pagebuilder/modules/simple_table.php
pagebuilder/modules/slider.php
pagebuilder/modules/tab.php
pagebuilder/pagebuilder.php
style.css