add namespace for world canvas handles

In the concert frameworld

world_canvas_server wouldn't start with default namespaces. like below 
Client would get problem with finding right services and topics.

```
/services/world_canvas/delete_map
/services/world_canvas/dynamic_map
/services/world_canvas/get_annotations
/services/world_canvas/get_annotations_data
/services/world_canvas/list_maps
/services/world_canvas/pub_annotations_data
/services/world_canvas/publish_map
/services/world_canvas/rename_map
/services/world_canvas/reset_database
/services/world_canvas/save_annotations_data
/services/world_canvas/save_map
/services/world_canvas/set_keyword
/services/world_canvas/set_relationship
/services/world_canvas/world_canvas_server/get_loggers
/services/world_canvas/world_canvas_server/set_logger_level
/services/world_canvas/yaml_export
/services/world_canvas/yaml_import
```
So I would like to add `world_namespace` parameter to configure world canvas client class.
I just changed python class. I was not sure how to change cpp client library.