Store graph layout on client machines

[johannesduesing]

Problem
Currently, the reuse graph will auto-layout everytime the website is opened. This makes it hard to highlight individual nodes, especially when visiting e.g. the details page before coming back to the main page.

Solution
It would be helpful to persistently store the node positions / graph layout in a client's local storage. This would enable users to "pick up where they left" when inspecting the graph.