WP Optimize Premium 3.7.1

* FIX: Prevent php warning and increase SendInBlue `mailin` plugin compatibility
* FIX: Avoid screen juggling while selecting optimizations from dropdown in scheduled clean up
* FIX: Prevent cache purge upon deactivation using filter
* FIX: Cache purge ability of all registered user
* FIX: Recognise WooCommerce product category images as used images
* FIX: Multisite support in `cached-file-log.php` template
* TWEAK: Improve Optimization Schedule UI
* TWEAK: Consolidated error notices by the use of a global WPO notice object.
* TWEAK: Remove `Reset WebP serving method` button when there are no webp conversion tools
* TWEAK: Remove query strings from scripts
* TWEAK: Add `Restrict Content Pro` plugin slug to `plugin.json`
* TWEAK: Add option to remove orphaned `user meta` data upon run optimization
* TWEAK: Add `no-cache` headers when minify is enabled and page cacheing is not
* TWEAK: Ability to remove `.htaccess` rules when gzip compression is not available
* TWEAK: WebP: Avoid PHP warnings when using hot linked images (Alter HTML method)
* TWEAK: WebP conversion is unavailable when php shell functions do not exist
* TWEAK: Improved UI settings for asynchronous loading and page speed testing exclusion tools
* TWEAK: Add a constant to enable/disable webp feature
* TWEAK: Set a global context for $wp_file_descriptions context so that it gets assigned to correctly, preventing a subtle visual change in the theme editor
* TWEAK: Prevent php warning from `webp-convert` library
* TWEAK: Update currently-active installs number in thank you for installing notice.
* TWEAK: Replaced deprecated use of jQuery.change()

* FEATURE: Import and export settings
* FIX: Avoid infinite loop while using unused images export csv
* FIX: Scheduled cache preloading issue
* FIX: WebP testing making unnecessary background HTTP checks
* FIX: Google fonts compatibility with The7 theme
* FIX: Prevent console error for undefined `wp_optimize` for smush scripts
* TWEAK: Avoid PHP warnings on cache cleanup
* FIX: Ability to disable webp serving while caching is on
* TWEAK: Reset webp conversion method flags daily using cron job
* TWEAK: Remove orphaned `wpo_weekly_cron_tasks` cron job upon uninstallation

* FIX: Build system error led to a missing file in 3.2.7 which could cause an error when using related functions
* FIX: Fix incorrect function name in admin class