Deprecated configuration fields and new messages

The sellerId, applicationId, and callbackUrl configuration fields are now deprecated. You now need to use the projectKey, applicationKey, and returnUrl fields respectively.
The new DeprecatedFields message will warn you if you use any of the deprecated fields.
Also, following the deprecation, the ProjectIsDeactivated message replaced the SellerIsDeactivated one, while a standard CORS error in the browser will replace the SellerNotFound message.

In addition, further new messages are available to receive feedback from more events.

Changes:

• Deprecated sellerId, applicationId, and callbackUrl fields.
• Added projectKey, applicationKey, and returnUrl fields.
• Added DeprecatedFields, ProjectIsDeactivated, CartWithExistingPayment, and OrderCreationError messages.
• Removed SellerIsDeactivated and SellerNotFound messages.