refactors in join to register complex aliases on duplicate, to do is doing the same in filter clauses

tests/test_models_helpers.py

@@ -0,0 +1,9 @@
+from ormar.models.helpers.models import group_related_list
+
+
+def test_group_related_list():
+    given = ['friends__least_favourite_game', 'least_favourite_game', 'friends',
+             'favourite_game', 'friends__favourite_game']
+    expected = {'least_favourite_game': [], 'favourite_game': [],
+                'friends': ['favourite_game', 'least_favourite_game']}
+    assert group_related_list(given) == expected