The following logic is used:
* first, display the completed Milestones (if requested),
in the chronological order in which they were completed,
* then the Milestones having a due date set,
in the chronological order in which they are due,
* lastly, all the Milestones that don't have a due date.
In the above groups, the ''natural sort'' order is used
in case of a tie
(e.g. a Milestone 0.9.4 would come before a Milestone 0.10).