Use macros to make the website as 'DRY' as possible

[butler54]

Issue description / feature objectives

There are a number areas where our website has definitions that we duplicate:

• Many links to external websites
• References to versions (trestle, oscal and dependencies)
• Some named entities

Ideally we want to define this references once across the project.

One way of doing this is with macros.

Caveats / Assumptions

• Rendered content should not change

Completion Criteria

• a significant subset of the material sought after has been covered
• website dev documentation is updated.