Scalability Pro 5.93

* Changed "Remove product cat dropdown" option to "Cache product cat dropdown" - now your quick edits will continue to work. Cache clears after 4 hours by default.

* Refactored plugin to be easier to maintain and update and add individual features
* Fixed 'woo onboarding' speed boost
* Further refactoring to move functionality into their own files to make the structure more logical
* Added new feature to let users disable the HTTP API calls that can add 10s to admin pages
* Renamed the tabs to be clearer
* Added custom query alteration options to start and stop various query optimisations on wordpress hooks - I'd appreciate feedback on this new option

* Updated cache handler to provide getCacheSize and deleteOldItems functions which provide group-specific functionality to aid SSF cache management

* Fixed warning on settings page for suppressed readlink error

* Fix for code hardening - hardening had come 2 lines too late, my bad

* Fixed warning for missing actionscheduler tables on empty install

* Fix for new settings to clear the local transient cache when the license key is changed
* Added a new 'recheck now' button on the license key page for when users renew or upgrade

* More settings warnings fixed

* Updated settings page interface - added logo, added context help
* Moved settings page to underneath Super Speedy
* Updated license checker code
* Minor optimisation in SQL_CALC_FOUND_ROWS code
* Updated SQL_CALC_FOUND_ROWS to not run for REST API requests - note: this will be reintroduced in future, but with a better solution. REST API calls tend to fetch page after page, so in their case, I could allow SQL_CALC_FOUND_ROWS on the first call, then cache the total count for page 2+ so that REST API exports would be faster

* Fixed remove group by option so that it ONLY applies to that dropdown
- @hakan found that filtering the wp-admin > product list by category was broken unless the cat was a top level cat