The product series page should show all milestones

In am momentary laps of reason, I decided to no show deactivated milestones without releases on the product series page. I was thinking of the old rule that an inactive milestone is dead, that is not so. If the owner wanted the milestone dead, he would delete it. For milestones, deactivated mean "it is not a target for bugs and blueprints".

This problem is most noticiable on https://edge.launchpad.net/launchpad-registry/2.2 where you can see in the timeline that there are many milestones, but you cannot see how much work was targeted to them or what their goal was.

Switch the page to use ProductSeries.all_milestones.