Update validators to use is_message_too_long()

- update check_sms_content_char_count to use the SMSTemplate.is_message_too_long function, and updated the error message to align with the message returned by the admin app.
- Update the the code used by version 1 of the api to use the validate_template method.
  - I did find a couple of services still using the old api, however, this change should not affect them as I checked the messages being sent and they are not too long.
  - We will be sending a message to them to see if they can upgrade.
- Update the log message for authenication to include the URL - makes it easier to track if a service is using version 1 of the api.

app/authentication/auth.py

@@ -125,10 +125,12 @@ def requires_auth():
         g.service_id = api_key.service_id
         _request_ctx_stack.top.authenticated_service = service
         _request_ctx_stack.top.api_user = api_key
-        current_app.logger.info('API authorised for service {} with api key {}, using issuer {}'.format(
+
+        current_app.logger.info('API authorised for service {} with api key {}, using issuer {} for URL: {}'.format(
             service.id,
             api_key.id,
-            request.headers.get('User-Agent')
+            request.headers.get('User-Agent'),
+            request.base_url
         ))
         return
     else: