Handle multiple IsPrimary tables in join building in CohortBuilder/Extraction based on IsExtractionIdentifier

[tznind]

Is your feature request related to a problem? Please describe.
Sometimes you want to join from one table to another e.g. CT_StudyTable to US_StudyTable within a narrow use case (e.g. a CohortBuilder query). But both are likely to be flagged as IsPrimaryExtractionTable since they can each be used in isolation within their own hierarchy (study=>series=>image).

Describe the solution you'd like
Query builder should attempt to pick a 'winner' when there are 2+ IsPrimaryExtractionTable. To start with this should be the table that has the IsExtractionIdentifier field.