SVG files, make theme specific versions of the svg files.

[homberghp]

Theme switching, for instance in dark mode changes the colors in the svgs

To be able to reason about the diagram, where the diagram uses color to distinguish element types,
we should add a legend of the color use in the diagram to each diagram.
Also do not refer to the colors by name, because e.g. green will render magenta in dark mode.

In the diagram below we added yellow and green for interfaces and classes