add visit_col, visitn_col and studyday_col` options

[jwildfire]

Main goal is to sync the settings as much as possible with other renderers. The new settings would be used to populate time_cols as follows:

if(settings.visit_col & settings.visitn_col){
  ordinal_time_col =   {
    "type": "ordinal",
    "value_col": settings.visit_col,
    "label": "Visit",
    "order_col": settings.visitn_col,
    "order": null,
    "rotate_tick_labels": true,
    "vertical_space": 100
  }
}
settings.time_cols.push(ordinal_time_col)

if(settings.studyday_col){
  linear_time_col = {
    "type": "linear",
    "value_col": settings.studyday_col,
    "label": "Study Day",
    "order_col": settings.studyday_col,
    "order": null,
    "rotate_tick_labels": false,
    "vertical_space": 0
  }
  settings.time_cols.push(linear_time_col)
}

[jwildfire]

@samussiah @pburnsdata You see any major issues with this approach?