Fixed node positions + automatic edge routing

[Nic30]

ELK now (0.9.0) supports automatic routing with fixed node positions. https://eclipse.dev/elk/blog/posts/2022/22-11-17-libavoid.html

It could be useful to to have mode where nodes could be dragged and edge routing could be regenerated. This functionality is also part of Xilinx Vivado.

However it may be possible that this requires an external library written in C++ which could be problematic. Because ELKJS is transpiled and ELK and this binary would not be available in browser.