Big refactoring: BaseDefinition._definnition changes to BaseDefinition._name, because it's a NamePart now.

This also includes changes to tests and some simplifications like deleting the old name logic of Definition.

test/test_evaluate/test_representation.py

@@ -5,7 +5,7 @@ from jedi import Script
 
 def get_definition_and_evaluator(source):
     d = Script(dedent(source)).goto_definitions()[0]
-    return d._definition.parent.parent, d._evaluator
+    return d._name.parent.parent, d._evaluator
 
 
 def test_function_execution():