Multiple bug fixes / Welcart extension plugin support / WP5.0 support

【Contents of fixes】
■Support for WordPress 5.0 (Gutenberg)
■Support extension plugins “WCEX Widget Cart”, “WCEX Order List Widget” and “WCEX Multi Price”.
■Changed the application range of the background color setting of the header bar (applied not only to the fixed display state but also to the normal display state).
■Fixed the bug that the header bar display position setting (for smartphones) is not reflected in some cases.
■Fixed a bug where the cart button in the header would not be displayed when the membership system was set to “Do not use”.
■Fixed a bug in the wording and output of the quick tag “Rounded Corner Button-S”.

The following files have been modified for this update.
【Corrected files】
functions/head.php
js/slick.min.js
language/ja.mo
language/ja.po
pagebuilder/pagebuilder.php
pagebuilder/modules/googlemap.php
pagebuilder/modules/image.php
pagebuilder/modules/simple_table.php
pagebuilder/modules/tab.php
pagebuilder/assets/admin/css/admin.css
pagebuilder/assets/admin/js/admin.js
pagebuilder/assets/admin/js/googlemap.js
pagebuilder/assets/css/pagebuilder.css
pagebuilder/assets/css/slider.css
pagebuilder/assets/js/googlemap.js
functions.php
header.php
style.css

【Added files】
wcex_olwidget.css
wcex_widget_cart.css