Add test to demonstrate that AVET vs EAVT inconsistency has been solved

[jonasseglare]

This MR adds an additional unit test to verify that the PR

#781

solved the EAVT vs AVET issue. If this unit test would be rebased on the commit before that PR, it will fail as follows:

Fail in test-load-taxonomy-data0

expected: (= eavt-sample avet-sample)
  actual: (not          
           (=
            #{[52 :relation/concept-1 48 536870921 true]}
            #{[49 :relation/concept-1 48 536870917 true]
              [52 :relation/concept-1 48 536870921 true]}))