sortlistmodel: Replace with an array-based model

sortlistmodel: Replace with an array-based model

This is the dumbest possible sortmodel using an array:
Just grab all the items, put them in the array, qsort() the array.

Some benchmarks (setting a new model):

  125,000 items - old: 549ms
                  new: 115ms
  250,000 items - new: 250ms

This performance can not be kept for simple additions and removals
though.