Woocommerce Sensei LMS 2.4.0

* New: Log that extension is installed
* Fix: Show confirmation notice on the Order Received page
* Fix: Replace call to deprecated WC Memberships method
* Sensei: Version bump to 2.1.0

* New: Restrict future updates for sites running a version of PHP less than 5.6 - #2502
* Fix: Conflict with Jetpack shortcodes module and Sensei videos - #2426
* Fix: Change progress status to "Completed" in modules (@tonytettinger) - #2432
* Fix: Lesson order changes when lesson is updated using Classic Editor - #2471
* Fix: Update version number on plugin update - #2503

* New: Add usage tracking for course enrolments
* Fix: PHP warnings when ordering courses, modules or lessons
* Fix: PHP warnings on Sensei Analysis page
* Fix: PHP warning on Course Results page
* Fix: Add missing translations on Messages screen
* Fix: Enable translating "more" text on Bulk Learner Actions screen
* Fix: Show post content for paid courses on single course page
* Fix: Show course categories in WordPress 5.0
* Fix: Coding standard and security violations
* Fix: Use updated lesson data when updating quiz
* Tweak: Removed underscores from filenames