Set free_sms_fragment_limit when creating a service

The free_sms_fragment_limit of a service is set when the service is
created. If a value for the free_sms_fragment_limit is not given, the
default value is used.

app/service/rest.py

@@ -138,6 +138,10 @@ def create_service():
         errors = {'user_id': ['Missing data for required field.']}
         raise InvalidRequest(errors, status_code=400)
 
+    # TODO: to be removed when front-end is updated
+    if 'free_sms_fragment_limit' not in data:
+        data['free_sms_fragment_limit'] = current_app.config['FREE_SMS_TIER_FRAGMENT_COUNT']
+
     # validate json with marshmallow
     service_schema.load(request.get_json())