WP Staging Pro 5.7.1

* New: Add multiple filters to keep existing media files, plugins, themes and mu-plugins after backup restore #1617
* New: Clean existing files during backup restore which are not in backup #1617
* Fix: Cloning does not work if php mb module is not installed #1669
* Fix: Catch fatal error happening on backup upgrade routine #1663
* Fix: Only process one backup queue action at a time. This make sure another action doesn't conflict with the backup action in process. Also fix the wpstg_queue backup processing table growing problem #1652
* Enh: Save log file name instead of complete task response in wp_wpstg_queue table. This reduces the size of backup queue table #1623
* Enh: Stop the backup job on critical errors during scheduled backup #1623
* Dev: Test for cleaning up files before backup restore fails on second run #1681

* New: Support up to WordPress 5.9.1
* New: Add filter wpstg.frontend.showLoginForm to allow third party plugin disabling login form for the staging site #1577
* New: Add labels to distinguish between network and single site clones on multisite
* Fix: Handle issue when showing staging sites in System Info #1560
* Fix: Fix Rows Generator for zero or negative values for Primary Key Index #1584
* Fix: Set option "Keep permalinks" on the staging site when updating a staging site if "keep permalinks" is active on the production site initially #1562
* Fix: Updating an existing multisite clone converted the clone to a single site #1565 #1589

* New: Create backups and restore of multisites #1458
* Fix: Force AnalyticsSender to convert wpstg_settings to array before usage #1559
* Fix: Backup Search & Replace does not work with new primary key conditional query #1556
* Fix: Fix labels on backup sites #1551
* Fix: Backup restore can not unserialize escaped serialized strings #1554