Widget: display details pane when node is clicked

[andrewedstrom]

Description

This adds a detail pane when a node is clicked, per https://github.com/Docmaps-Project/docmaps/issues/130

It also makes it so when there are too many nodes to fit on screen, the svg viewport is zoomed out to fit them all.

Related Issues

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Checklist

• [x] I have tested these changes locally and they work as expected.
• [x] I have added or updated tests to cover any new functionality or bug fixes.
• [ ] I have updated the documentation to reflect any changes or additions to the project.
• [x] I have followed the project's code of conduct and conventions for commit messages.

Additional Information

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