Ported interface.
Added ability to write gedcomx files in zip format with manifest attributes.
Merge branch 'Sprint'
Updated RS API to use GX File for serializaation processing.
Merge branch 'Sprint'
Ported builder methods for models.
Fixed null known type assignment.
Ported missing interface. Added extension element tests.
Fixed test for source references.
Test cleanup.
Updated GEDX file unit tests.
Merge branch 'master' into FixOverrideMethods

* master:
  Updated GEDX file unit tests.
  Test cleanup.
  Fixed test for source references.
  Ported missing interface. Added extension element tests.
  Fixed null known type assignment.
  Ported builder methods for models.
  Updated RS API to use GX File for serializaation processing.
  Added ability to write gedcomx files in zip format with manifest attributes.
  Ported interface.