Layout Persistence

[jaads]

The dagre layout is good to get a first hierarchical layout calculated. However, I found myself move nodes around to get a better understanding of the structure. Since the layout is not getting persistent at the moment, the next time I open the diagram, the default dagre layout is used.

Therefore, it might be nice to store the node positions for a custom layout.

[jaads]

This would also have a nice side-effect: For larger graphs the layout calculation is currently a bottleneck (see benchmark) where is could take several seconds to calculate it. By having the layout persistent, this heavy calculation would only need to be done once