Fixed Notice error/added custom script function

【Contents of the fix】
■Fixed the Notice error in the theme options “Top Page” and “Plan”.
■Added custom script function in the theme option “Basic Settings”.

The following files have been modified for this update.
【Fixed files】
admin/inc/basic.php
admin/inc/plan.php
admin/inc/top.php
inc/head.php
languages/ja.mo
languages/ja.po
style.css