WP Staging Pro 5.4.2

* 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

* New: Support for WordPress 5.9
* New: Add filter to change the cache folder for creating & restoring backups #1528
* New: Huge performance improvement for search & replace in cloning / pushing / backup process #1522
* Fix: Call to undefined function human_readable_duration() on backup creation if WP is older than 5.1 #1527 #1525 #1535
* Dev: Add unit tests for Times class
* Dev: Update db_version in SQL dumps to match WordPress 5.9 db version #1539
* Dev: Add command to get db_version from database