Associated Person Domain Handling

Currently there is not logic to override USUBJID in favor of APID for AP-- datasets. We need to go into the library metadata logic and use the dataset_metadata.is_ap property to override in this case.

As @pendingintent also pointed out-- there also may be some issues with required variables not being such for the AP counterpart of certain domains. He is doing research for this. If they do inherit the requirement, no change is need but if not, we will need to work a solution out (potentially adding AP and using is_ap to ID for scoping inclusion/exclusion criteria and selectively excluding AP from required variable rule checks would be a potential solution)