sortlistmodel: Use timsort

sortlistmodel: Use timsort

Simply replace the old qsort() call with a timsort() call.

This is ultimately relevant because timsort is a LOT faster in merging
to already sorted lists (think items-chaged adding some items) or
reversing an existing list (think columnview sort order changes).

Benchmarks:

    initially sorting the model
                    qsort  timsort
    128,000 items   124ms    111ms
    256,000 items   264ms    250ms