Increase speed of creating and opening clusters (for large networks).

[holdenli]

I have a network for ~1k nodes and edges. I'm using a hierarchical layout and disabled physics to increase performance. The initial draw takes 2 seconds according to Chrome profiling tools which is fine with me.

However, I want to add interactive buttons for clustering. Both creating and opening clusters takes 2 seconds as which makes the page feel very unresponsive. According to the profiler, a majority of time is spent in layout code (eg. minimizeEdgeLengthBottomUp). These are very small clusters, can we optimize it so we don't recalculate the whole network for clusters?

PS - I also want to create dozens of clusters immediately upon page load but with each one taking 2 seconds this causes page to freeze up.