Implementing full encoding and decoding support for References

[piotrszul]

Resolves #1784

[johngrimes]

This is the error that occurs if you try to traverse to assigner within an Identifier within a Reference:

pyspark.errors.exceptions.captured.AnalysisException: [FIELD_NOT_FOUND] No such struct field `assigner` in `id`, `use`, `type`, `system`, `value`, `period`, `_fid`.

I think this is fine for now.