YITH Product Size Charts for WooCommerce Premium 1.8.0

* New - set the Tab title of Size Charts
* New - support to WooCommerce 3.4.x
* New - support to WordPress 4.9.6
* Update - Italian language
* Update - Dutch translation
* Update - Spanish translation
* Update - plugin framework

* New - Spanish translation
* Tweak - fixed links
* Fix - issue when duplicate Size Charts containing quotation marks
* Dev - added yith_wcpsc_table_header_content filter
* Dev - added yith_wcpsc_table_content filter

New - support to WooCommerce 3.3
New - possibility to print the Size Chart table by using the shortcode
New - shortcode metabox in product size charts
New - Dutch language
Update - Plugin Framework
Dev - added yith_wcpsc_apply_the_content_filter filter