Multiple bug fixes

【Contents of the fix】
■Fixed a bug in which the transition to the external link payment screen did not work for a specific payment system (Epsilon) and returned to the previous screen.
■Fixed a button replacement error on the cart confirmation page.
■Fixed a bug that the “pagination display style” setting in Theme Options > Blog > Post Details was not saved.
■Fixed a minor error.

The following are the files that have been modified for this update.
【Corrected files】
・admin/inc/blog.php
・funtions/welcart.php
・funtions/welcart_cf.php
・template-parts/index-slider.php
・wc_templates/wc_item_single.php
・style.css