Woocommerce Authorize.net CIM 3.10.8

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

* Fix - Clear cached Client Keys when saving settings to prevent stale keys from being used
* Fix - Ensure the CSC field is passed to Accept.JS when enabled

* Feature - Unify the functionality of Authorize.Net AIM, SIM, and DPM into a single plugin
* Feature - Add an optional lightbox hosted credit card payment
* Feature - Add Accept.js support and an optional hosted payment form for eChecks
* Feature - Streamline setup to use Accept.js by default with no extra configuration required
* Feature - Add migration support for settings and data from AIM, SIM, and DPM
* Tweak - Send order address fields with refunds to decrease the chance of errors
* Fix - Prevent errors when product names or descriptions contain HTML and exceed the length limit
* Misc - Remove support for WooCommerce 2.6
* Misc - Require PHP 5.6+