Add `ncol` or `nrow` to `plot.see_check_model()`

[mattansb]

The plot for check_model() is quite "tall" - would be nice to have it wider, or better yet - controllable by the user.

[strengejacke]

For now, you can return each panel as single plot and compose it in a way you want. But we have:

  if (panel) {
    pw <- plots(p, n_columns = 2)
    .safe_print_plots(pw)
    invisible(pw)
  } else {
    return(p)
  }

so we could simply add an n_column argument (not sure right now how this is named in other functions, but we have this in several plotting functions).

[bwiernik]

I'll add arguments to control the dimensions

[strengejacke]

We have an n_column argument now.