Dynamic transaction graph using Sprotty

[tilk]

Sprotty is a pretty cool diagramming framework, which could be used for dynamic exploring of the transaction graph. Unfortunately, the static graphs we can currently generate have lost some readability due to increasing complexity of the core.

I started some work but stumbled on a weird issue involving positioning of nodes and edges when some nodes are embedded inside others. The elklive service seems to handle that well, so this should be doable.