[AddonFlare] Paid Registrations 1.4.5

Bug Fixes:
- Fixed bugs + improved compatibility with the latest Stripe API
- Fixed an issue with PayPal that would sometimes not redirect back to the registration page
- Fixed a potential bug that wouldn't allow guest purchases if the "view" general user group permission was set to never for guests

New Features:
- Added a check to require unique emails for the initial "email" input (for guest purchases)
- Added an option to force the user to complete registration with the email that was first inputted (disallow modifying email in registration form)