gbXML translation does not roundtrip unless Facility object present

[macumber]

The following code will fail unless the model has a Facility object present

  ForwardTranslator forwardTranslator;
  bool test = forwardTranslator.modelToGbXML(model, p);

  EXPECT_TRUE(test);

  // Read the XML back in and check the surface
  ReverseTranslator reverseTranslator;
  boost::optional<Model> model2 = reverseTranslator.loadModel(p);

  ASSERT_TRUE(model2);

Also, Spaces will not be translated without a Building.