`DataColumn.sortWith()` function

`DataFrame`s have the `sortWith` function which allow you to write a `Comparator` to sort the rows. `DataColumn`s currently only have `sort()` and `sortDesc()` if the type is a `Comparable`.
If you want to sort a `DataColumn` separately, you would first need to convert it to a `List` or `DataFrame`. IMO, this is a missed opportunity in the API. 