Make response headers available to the code generator (tryout)
"External Documentation Object" implemented (according to spec)
Unittests fixed

* ModelConverterTest, ScalaModelTest: the properties ordering is different (alphabetic as it seems)
* ParameterSerializationTest: comparison failed because of CR/LF (could also be an OS-related problem)
* CompositionTest did never work in history (maybe an implementation code is missing?)