WooCommerce Cart Notices 1.16.1

* Misc - Add support to WooCommerce 3.6
* Misc - Require PHP 5.4+

* Misc - Drop support for PHP 5.2: PHP 5.3 is now the minimum supported version
* Misc - Update SkyVerge plugin framework to version 5.3

* Dev - Introduce `wc_cart_notices_notice_message` filter