DropdownColumnSpec
class DropdownColumnSpec<T, S : Comparable<S>>(headerName: String, widthSetting: WidthSetting, valueSelector: (T) -> S, val valueFormatter: (S) -> String = { it.toString() }, val choices: List<S>, onEdit: (rowIndex: Int, newValue: S) -> Unit? = null) : ColumnSpec<T, S>