Cannot delete Entitites associated with multiple Datastreams

[SpeckiJ]

If a Thing is linked to multiple Datastreams, or two Datastreams reference the same Dataset, deleting it fails due to ConstraintViolationExceptions.

o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: update or delete on table "dataset" violates foreign key constraint "fk_dataset_datastream" on table "datastream_dataset"

This is caused by the cascading delete failing to delete the underlying dataset as it is still linked to other entities.

[SpeckiJ]

This will be no problem for v2 after db-model is updated to version 4.x as the relation is completely refactored there