Multiple bug fixes / support for WP5.8 widget block editor

【Contents of the fix】
■Support for the WordPress 5.8 widget block editor
■Fixed a bug in the “Blog List” of the fixed page that the category and date were not displayed even if the checkbox to display them was checked.
■Fixed a bug in the TCD theme options.
■Fixed an error that sometimes appears in the comment section and SNS icons.
■Supports the “Contact Form 7 Multi-Step Forms” plug-in.

【Modified files】
admin/inc/page.php
css/design-plus.css
functions/category.php
functions/page_ad_post_list.php
languages/ja.mo
languages/ja.po
template-parts/sns-btn-btm.php
template-parts/sns-btn-top.php
functions.php
style.css