Wicket.Window.unloadConfirmation has been removed

"In Wicket 6 a new setting has been added to ModalWindow: #showUnloadConfirmation(). In Wicket 7 the new Java API should be used instead of dealing with the JavaScript property Wicket.Window.unloadConfirmation."

Impact: small, found 3 usages of Wicket.Window.unloadConfirmation in the code base.