Python bindings for the drake_ros_viz package may not cover the complete public API

[gbiggs]

The drake_ros_viz package added by #23 has some Python bindings added in #24. These Python bindings are sufficient to set up a visualiser system and connect it to a Drake system, as shown here.

However, it may give users more flexibility and feature availability if the remaining API of this package is made available via Python bindings.

This task is to investigate the remaining API of drake_ros_viz and determine if any of it is/should be public API, and then create Python bindings for the API calls and types that are identified as public.