Merged the "accounting.base_account.models" and "accounting.account.models" modules into the new "accounting.modules" module, so that the data models can reference one another.

tests/test_base_account.py

@@ -54,7 +54,8 @@ class BaseAccountTestCase(unittest.TestCase):
 
         :return: None.
         """
-        from accounting.base_account.models import BaseAccount, BaseAccountL10n
+        from accounting.models import BaseAccountL10n
+        from accounting.models import BaseAccount
         runner: FlaskCliRunner = self.app.test_cli_runner()
         result: Result = runner.invoke(args="accounting-init-base")
         self.assertEqual(result.exit_code, 0)