add interfaces and enums for AddBooking use case
fix references to other objects in interfaces
implement interfaces in model
wrap if-return-null in curly brackets
add constructor with interface to domain classes
add basic ModelControllers
started work on CreateBooking use case
fix persistence for CreatePaymentContracts, and

implement some NotImplemented methods
add system operations until ConfirmPayment

CreateBooking just about done?
Merge pull request #8 from TBroedsgaard/AddBookingModel

AddBooking model