Add option to switch convergence graph from showing electronic to only ionic steps

[janosh]

On relaxations that require many ionic steps like https://materialsproject.org/materials/mp-1033715/tasks/mp-1033715, showing each electronic step may be too much information, making the convergence graph hard to read.

Would be nice to have the option to toggle between electronic and ionic steps. The toggle should default to only ionic steps on long trajectories.

Related discussion

https://github.com/materialsproject/crystaltoolkit/pull/323#issuecomment-1493380382