WooCommerce Lightspeed POS Integration 2.16.6

* New - Much better handling around 429 errors - now keeps track of Lightspeed's API bucket level header, and adjusts API requests dynamically depending on bucket level
* New - New "Prune deleted variations" setting. On a Manual Update, deletes variations in WooCommerce that have been deleted in Lightspeed matrix products.
* New - New "WCLSI Poller" settings, allows users to turn background job on or off
* New - Settings UI is now tabbed
* New - wclsi-error.log now has a stack trace included in it
* New - Updating Variations in the WooCommerce dashboard is now more efficient and should not cause as many 429 errors
* Fix - Fixes some DB duplicate errors that can happen during the check_for_new_ls_prods background job, now checks if the product exists before trying to insert it
* Tweak - Code consolidation and cleanup

* New - New "wclsi-error" log under WooCommerce -> Status -> Logs; tracks sync errors and other various issues with the plugin
* Fix - If multiple items are added to the cart, the plugin would get a 429 error trying to check inventory levels in Lightspeed
* Fix - On checkout, the plugin can now handle updating multiple items on checkout/order completion
* Fix - Bulk updates on import page are now throttled and should no longer show 429 errors
* Fix - Image sync would throw a fatal error, now should write to error log
* Fix - Hotpatch for fixing NULL item_id values (only fixes simple/single products)
* Tweak - wclsi-debugger.log will now only record active sync changes, instead of all activity
* Tweak - Code cleanup & optimizations

* Fix - Fixes a major bug where WooCommerce products that have sync enabled were not pulling LightSpeed inventory before checkout