Create an initial Py Trees node

Related to #85

User Story/Description

As a developer I need a running state machine/behaviour tree in order to facilitate future work for competition tasks.

Definition of Done

A launch file (e.g. pytrees.launch.py) starts an empty node that imports PyTrees and creates a root node in the tree that does absolutely nothing.

How

1. Install Py Trees in the intelligence Dockerfile
2. Create a new python node in the lhw_intelligence package
3. Import and create an empty root tree in a ROS node
4. Create a launch file that launches the previous node