IMPROVEMENT: Inconsistency in Code

[agy-why]

In https://github.com/django-daiquiri/daiquiri/blob/master/daiquiri/oai/adapter.py#L206

There is an inconsistancy between the naming of the classes:

• DatalinkOAIAdapterMixin (correct?)

vs

• BaseOaiAdapter
• MetadataOaiAdapterMixin
• RegistryOaiAdapterMixin
• DefaultOaiAdapter