Ability to Assign a Waiter to an Order

Starting from V6, it will be possible to specify a waiter when creating an order, as well as change the waiter later.

In versions up to and including V5, the user on behalf of whom the plugin operates was automatically assigned as the waiter for all orders created by the plugin, and it was not possible to change the waiter via the API afterwards. Starting from V6, the CreateOrder method will have an optional argument that allows specifying a different waiter (by default, the current user will still be the waiter), and a ChangeOrderWaiter method will be added, through which a new waiter can be assigned.