KPI counting accessions

I'm trying to define a KPI Execution to count the "Number of accessions documented in published Datasets".

• Parameter: Dataset with state = 'PUBLISHED'
• No dimensions.

Execution fails with illegal attempt to dereference collection [dataset0_.id.accessionRefs] with element property reference [accession].

This is because Dataset#accessionRefs is a collection and needs to be joined (as documented https://stackoverflow.com/questions/24750754/org-hibernate-queryexception-illegal-attempt-to-dereference-collection/24751098#24751098).

Fix

We should introduce something similar to the link property in ExecutionDimension to the Execution to declare the join.