[FEA] Implement a good serialization approach for transfering host data between Java and JNI

[ttnghia]

Currently, we don't have a good way to transfer host data between Java and JNI. As such, most of the time we have to manually do reflection to get access to the Java object in JNI code. That is very inefficient and not suitable for transferring large amounts of objects.

We should have a better way for data transfer between Java and JNI. Maybe leveraging protocol buffer, or implementing our propriety data serializer/deserializer.