Refactor system diagram build to use redo

Created by: erlehmann

This PR refactors the system diagram build to use redo.

Advantages:

• build.sh now builds before waiting for changes
• Separation of concerns in build scripts
• Targets can be build separately

Disadvantages:

• New dependency on redo.
  • This could be remedied by including Avery Pennarun's “do” script.