Figure hangs when plotting using default options

# Description

The figure used for `SimplexPlotterMixin` hangs when using the default options. However, I don't believe this issue is with the `SimplexPlotterMixin` figure at all. I believe this is to do with how `SimulationRunner` calls the command for optimization.

# Proposal

`SimulationRunner.run_simulation` currently uses `subprocess.call` to run the model that we're optimizing. By changing this to `subprocess.Popen` and repeatedly updating the figure/polling to see if the job ended we can mitigate this hang.