Fixed multiple bugs

[Contents of fixes] Basic Settings
■Fixed a bug in the show/hide setting in Theme Options > Blog > Pickup Articles List and Related Articles List.
■Fixed the thumbnail size of the article list.
■Fixed the breadcrumb list.
※Theme Options > Blog > “Text to display in breadcrumb list” is now hidden if it is blank.
■Fixed a bug that you can’t change the font size of the body text on smartphones.
■Fixed the bug that the Meta title and Meta description of the article are not reflected.
■Updated the theme options management feature.
※It is now possible to import sample articles, sample categories, sample global menu, and sample widgets by checking the checkbox when applying the theme to a new site or resetting the theme options.

The files that have been modified for this update are as follows
【Fixed files】
・admin/theme-options.php
・admin/inc/basic.php
・admin/inc/header.php
・admin/inc/tools.php
・functions/custom_editor.php
・functions/seo.php
・languages/ja.po
・languages/ja.mo
・template-parts/breadcrumb.php
・author.php
・functions.php
・header.php
・single.php
・responsive.css
・style.css
【Added files】
・img/op_default/image_260x180.gif
・img/op_default/image_300x250.gif
・img/op_default/image_800x550.gif