[trees] optional node, node name arguments to the tree setup

[stonier]

• [x] Resolves #181
• [x] Replicates the part of #182 relevant to node and node names

[stonier]

• I need to get some full tree tests happening in this repo → #189.
• Verified that py-trees-blackboard-watcher still discovers it automatically, despite blackboard services moving:

/foo/blackboard_streams/close
/foo/blackboard_streams/get_variables
/foo/blackboard_streams/open
/foo/describe_parameters