Resolved the inconsistency in response formats between the Python Ech…

…o bot template and the C# and JavaScript Echo bot templates. (#2124)

generators/app/templates/echo/{{cookiecutter.bot_name}}/bot.py

@@ -9,7 +9,7 @@ class MyBot(ActivityHandler):
     # See https://aka.ms/about-bot-activity-message to learn more about the message and other activity types.
 
     async def on_message_activity(self, turn_context: TurnContext):
-        await turn_context.send_activity(f"You said '{ turn_context.activity.text }'")
+        await turn_context.send_activity(f"Echo: '{ turn_context.activity.text }'")
 
     async def on_members_added_activity(
         self,