Now that we fleshed out the notion of what a customer is, it is easier to create more than one.
In fact for this task we already made an array of multiple customers.

## Model

In our model we now have an array with different customers to be served.
But we now have to handle the case, where the cashier gets a new customer.
For that we added a new state STATE_ready_for_customer

## Task

Your task is to implement, that, if a customer is finished, the cashier gets a new one.