MailChimp for WooCommerce Memberships 1.5.0

* Tweak - Open documentation link in settings in new tab
* Fix - Make sure a member is synced on user profile updates not only when updating their email address
* Misc - Change "List" to "Audience" per Mailchimp terminology update

* Fix - Ensure all available lists are offered in the settings and not limited to the first 10

* Fix - Do not sync manually created memberships that have not been saved yet for the first time and have still an auto-draft status
* Fix - Do not sync a user updating details at checkout if they don't have any membership yet
* Misc - Add support for WooCommerce 3.6
* Misc - Require PHP 5.4+