Update/introspection nodes

[Timple]

On behalf of @RichardK

• don't spin inside the node, let the outside user determine how to spin this node and how to catch exceptions properly
• Fix encoding/ decoding of user_data messages. This most likely also fixes the "set as initial state" button in the smach_viewer
• updated test accordingly
• set_initial_state was called inside a callback, so rate.sleep() is replaced by time.sleep() (see rate docs)

These changes are verified on running robots together with: #116