Navaids: allow persistence of builder models

[davidwatkins73]

Description

Currently we have to cut n' paste from the output to the svg_diagram table. We should also persist the underlying model data so diagrams can be easily tweaked.

Resourcing

We intend to contribute this feature

[davidwatkins73]

Tasks:

• [x] Add svg diagrams to the list of supported EntityKind types
• [ ] Update diagram builder to save to an entity note (the notes should be hidden, i.e. the section not shown)
• [ ] Persist the diagram contents to the svg_diagram page