Telegram refactoring:

- Fixes zammad#2289 - Added Telegram video support.
- Improved error handling via raise Exceptions.
- Removed unused methods.
- Fixed typos.
- Improved messages to client - return status: :ok even if the message could not be processed. This stops the Webhook loop for these message.

app/controllers/channels_telegram_controller.rb

@@ -67,7 +67,11 @@ def webhook
     end
 
     telegram = Telegram.new(channel.options[:api_token])
-    telegram.to_group(params, channel.group_id, channel)
+    begin
+      telegram.to_group(params, channel.group_id, channel)
+    rescue Exceptions::UnprocessableEntity => e
+      Rails.logger.error e.message
+    end
 
     render json: {}, status: :ok
   end