filter_model_ensemble_plot: Plot traces for ensemble members in a filter model fit
In rplzzz/CovMitigation: COVID-19 infection model for Virginia

This plot requires that the history was kept in the filter fit.

filter_model_ensemble_plot(
  filterfit,
  what = "fi",
  Nplot = 50,
  highlight = NULL
)

`filterfit`	Filter-fit object
`what`	Variable to plot (fi, beta, ncase, import_cases). Default is `fi`. If ncase is selected, then the observed effective case counts will be plotted as points.
`Nplot`	Number of ensemble members (randomly selected) to plot. Default is to plot 50. If `NULL`, then plot all.
`highlight`	List of ensemble member ids to overplot in a highlight color. Default is none.