WooCommerce Measurement Price Calculator 3.23.6

* Fix - Use core WooCommerce loader function to include settings classes to prevent possible conflicts with some third party plugins
* Dev - Adds a variation arg to the wc_measurement_price_calculator_measurement_needed_surface_area and wc_measurement_price_calculator_measurement_needed filters

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

* Fix - Remove potential PHP errors by gracefully bailing out on edge cases where product measurement values are null
* Fix - When ordering again a product, make sure cart price determined from measurements is correct if the originally ordered item is a product variation
* Fix - Address a JavaScript browser compatibility issue with Microsoft Explorer
* Dev - Introduce a filter hook to modify the final calculated price for an item with measurements
* Misc - Drop support for PHP version 5.2: PHP 5.3 becomes the minimum supported version
* Misc - Update the SkyVerge Plugin Framework to version 5.3