Suggestion: allow expanding / collapsing nodes in railroad diagram view

[zspitz]

For example, in the following railroad diagram: there should be some way to expand the LineContinuation node to its full definition, in-place: One issue: how should the expand be triggered? If this was the only possible interaction, then I would suggest clicking on the node should expand (what about collapse). However, perhaps clicking should be reserved for navigation within the railroad diagram view (#25); this would require some kind of additional UI.

[mike-lischke]

I guess this will require to rewrite this script and use D3.js (like for the other ones). Not sure when I can find the time for that.