juwang - Add methods for serializa/deserialize file for ProtocolBufferClassHierarchy

Currently protobuffer class hierarchy serialization/deserialization is on the ClassHierarchy object. In order to share the serialized result cross languages, especially serialize a class hierarchy in Java, then deserialize it in C#, this PR added two methods in ProtocolBufferClassHierarchy class. 

- public static void serialize(final String fileName, final ClassHierarchy classHierarchy)
- public static ClassHierarchy deSerialize(final String fileName) 

TestClassHierarchyRoundTrip is updated to for round trip testing between serialized files for all the scenarios.