updated roadmap based on feedback from MITRE TAXII team
Added unit tests for good and invalid Success messages
Fixed test and added TODO on mapping status detail and extended headers

Issue is that a list of strings in a mixed content field collapses
to a *single* text field on marshalling.
Renamed constants

Also implemented interfaces that hold constants rather than
repeating the interface name everywhere.
Added StatusMessage.createStatusDetailDetail(name, value)

Also added a unit test for Destination Collection Error