Re-Implement graph display for processes

We'd like to get our graph back 🙏

The idea here is to replace d3 usage by something lighter: using SVG to display the graph, and a library to calculate positions (using force directed layouts).

Here is a seemingly barebone libray (used by other higher level tools) with few deps : https://github.com/anvaka/ngraph.forcelayout

Features we want:

• render any process graph (so directed acyclic graph)
• a node can be highlighted (click on a summary item)
• a node can change of style (state updates)
• a node can be clicked and triggers an event