Added initial DAPOrderProcessing C# project
Added DAPOrder processing unit test project
Referenced xUnit in DAPOrderProcessing.Tests project
Adding items to an order + unit test
Not allowing adding of items when order is payed or cancelled + unit tests
Implementing business rule "You can only pay for an order with a least one item" + unit tests
Implemented business rule "You can only pay for an order which was not already payed" + unit tests
Implemented business rule "You cannot remove items from an empty order" + unit tests
Implemented business rule "You cannot remove items from payed or cancelled order" + unit tests
Implementing business rule "You can only cancel an unpayed order" + unit tests
Implemented business rule "You cannot pay for a cancelled Order" + unit tests
Implemented business rule "Only payed order can be completed" + unit tests
Implemented business rule "No operation is allowed on completed order" + unit tests