Check for duplicate keys in config file (#1511)

* Check for duplicate keys in config file
* Corrected BDD tests
* Unneeded check removed
* Make use of ruamel DuplicateKeyError exception
* Remove unneeded import and function
* slightly reword warning message
* fix merge conflicts
* update tests

Co-authored-by: Jonathan Wren <jonathan@nowandwren.com>

jrnl/messages/MsgText.py

@@ -198,6 +198,13 @@ class MsgText(Enum):
         Configuration updated to newest version at {config_path}
         """
 
+    ConfigDoubleKeys = """
+        There is at least one duplicate key in your configuration file.
+
+        Details:
+        {error_message}
+        """
+
     # --- Password --- #
     Password = "Password:"
     PasswordFirstEntry = "Enter password for journal '{journal_name}': "