Ability to provide selected choices in select_group_ui

[filipwastberg]

It would be neat to be able to provide selected values for each virtualSelectInput like this:

select_group_ui(
          id = "my-filters",
          params = list(
            list(inputId = "Manufacturer", label = "Manufacturer:", selected = "Acura"),
            list(inputId = "Type", label = "Type:")
          ),
          vs_args = list(
            disableSelectAll = FALSE
            )
        )

This way users could get a more custom made start view of an app.