WPMU DEV - Snapshot Pro 4.21.1

- New: Make Hub work with v4
- Fix: Issues with restoring backups when there are tables with the wrong db prefix
- Improvement: Enhance handling of large files in backups
- Fix: Issues with masking login area when restoring backups
- Fix: Issues with deleting failed backups
- Improvement: Prevent backup delays when large sites are being processed
- Improvement: Enhance UX while a backup is being triggered
- Improvement: Enhance UX while a schedule is being saved
- Improvement: Remove unused info from API responses
- Fix: PHP v5.6 issues

[New] Add upgrade to 4.0 prompts in Snapshot 3.0

Fix: Backups not uploading and old backups deleting when Storage Limit = 0
Fix: Snapshot backups not including media files for sites hosted with FlyWheel