Online registration simplification

If you have already invited a customer with the online booking invitation, they can now also complete a regular registration.

If you have already invited a customer with the online booking invitation, the customer could not complete a regular registration under this email address and had to complete their registration via the "resend registration email" function. This behavior has now been changed so that they can also complete a regular registration.

This makes it easier for the customer to book their next appointment.