Add PayPal webhook handler and marketing styles

- Implemented PayPal webhook for handling payment notifications, including signature verification and transaction updates.
- Created invoice generation and license management for software upgrades upon successful payment.
- Added comprehensive logging for debugging purposes.
- Introduced new CSS styles for the marketing file management system, including layout, toolbar, breadcrumb navigation, search filters, and file management UI components.

settings/settingsmenu.php

@@ -336,6 +336,7 @@ $page_rows_invoice = 25; //invoices
 $page_rows_dealers = 25; //dealers
 $page_rows_software_versions = 50; //software versions
 $page_rows_software_assignment = 50; //software assignment
+$page_rows_folders = 25; //marketing folders
 
 //------------------------------------------
 // Languages supported