Add dot-generated SVG diagram of module dependencies - WIP

[timbl]

This branch has an independent subdirectory where the various operations to grab dependencies and plot them happen. the code worked by looking at lines with require r import but may need updating to recognize newer forms of import.

[angelo-v]

We should try existing tools like depcruiser, which work quite fine in my experience. The diagram generation can then be part of the build and visualizations can be deployed to gh-pages