IMPROVEMENT: missing relation between datlink entries and releases

[agy-why]

There is no clear way to relate a datalink entry with a given release.

However this relation does exists. Each datalink table (non-generated ones) leaves in a schema (representing the release).

A solution would be to propagate the schema information down to OAI via the oai datalink adapter:
https://github.com/django-daiquiri/daiquiri/blob/master/daiquiri/oai/adapter.py#L206

The schema information is stored in the table name. From this one could extract the published and updated dates but also the IsPartOf entry without the necessity of a specific semantic from datalink.

This would only require to put the datalink table in the proper schema (representing the release).

[agy-why]

related to #209

[agy-why]

To get updated and published date for an object with DOI, read published and updated date from metadata of the corresponding datalink table (the one holding the doi).