Replacing java.lang.Date with joda time DateTime
Adding optimistic tests for Invoice
Adding DropWizard dependency and creating an entry point LokeService
Adding InvoiceResource to service.

Creating and adding InvoiceResource to the service and defining
documents for communication in no.encodia.loke.invoice.api
Extracting creditorName and creditorAccount to an object of it's own,
creating a clearer api