Support edge_data dictionary in the graph data structure

[RazinShaikh]

This is analogous to vdata and can be used for storing arbitrary data corresponding to an edge. For example, storing edge curve information in ZXLive (see zxcalc/zxlive#270), future support of multiplier edges, etc.

[jvdwetering]

So it is definitely an option to store it in edge data. But seeing as we now also have Edge objects, it might also just be part of the Edge? Although then it won't be available to GraphS, so that's probably not ideal.

[RazinShaikh]

Do you mean store curve distance in the Edge class or an edge data dictionary in the edge class?

[jvdwetering]

Maybe just edge_data in the Edge class. But for consistency, since there is a vertex_data in the Graph, maybe we should also have a edge_data.