Continued refactoring the serialization tests

* Standardized naming in SerializationTests
* Abstracted the roundtrip procedure into helper methods
* Extracted test classes and helper methods into SerializationTestHelper
* Removed YamlTest.YamlText since it is now unused
* Renamed YamlTest and changed from inheritance to direct static method invocation
Changed yaml files with tags for local types into templates

* This makes tests more robust to changes
* Also removed converter.yaml since it is not used
Got rid of empty.yaml
Renamed test helper classes

* Removed the Person class and used Simple (formerly Z) instead
The (De)Serializer helper properties use a common instance during each test method