payment window elements created (dummy objects at the moment, just shows stuff)
PaymentFrame: calculations and buttons work, only have to implement saving the purchases (SalesDomaindControllerImpl).

Almost didn't touch PurchaseTab.java - damn autoformatter :(
SalesDomainControllerImpl.submitCurrentPurchase() done - spent easily over an hour for it, was super easy actually..

now have to check exceptions only and maybe layout