Implemented ConceptManager with concept creation, modification and deletion

tests/parsers/test_DefConceptParser.py

@@ -503,6 +503,15 @@ from give me the date !
         assert context.sheerka.isinstance(res.value, BuiltinConcepts.UNKNOWN_CONCEPT)
         assert res.value.body == ("key", "unknown")
 
+    def test_i_cannot_parse_bnf_definition_referencing_multiple_concepts_sharing_the_same_name(self):
+        text = "def concept twenty one from bnf 'twenty' one"
+        sheerka, context, parser, *concepts = self.init_parser(Concept("one", body="1"), Concept("one", body="1.0"))
+        res = parser.parse(context, ParserInput(text))
+
+        assert not res.status
+        assert context.sheerka.isinstance(res.value, BuiltinConcepts.CANNOT_RESOLVE_CONCEPT)
+        assert res.value.body == ("key", "one")
+
     @pytest.mark.parametrize("text", [
         'def concept "def concept x"',
         'def concept "def concept x" as x',