Multisystem debug

Description

This MR adds the 'multisystem_debug' module, which provides routines to write output to generate the propagation diagrams. This output is written to debug/propagation.txt which can be read in directly from the web page, or can be further processed into a JSON file by the timeline.py script (part of the octopus_documentation repository).

News snippet

Generate debug output for propagation diagrams.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.