Draft: Added unit test to run behavior trees

[marip8]

Adds a unit test to load and run the defined behavior trees:

To-do:

• The unit test requires a QApplication to be created for the widgets, which cannot be done on a headless computer (e.g., CI runner).
• The unit test checks that all defined nodes can be loaded/created, but it only runs the trees defined in the current XML file. This means that not all of the nodes get triggered and thereby tested. It is also non-trivial to test nodes individually because some need artifacts produced by other nodes (e.g., tool paths, home joint state messages, etc.)