Report queue window in status JSON.

In order to render queue window information nicely in status pages pass
the window for each queue in the JSON status blob. Also, annotate each
change in a queue with an active flag indicating whether or not it is
currently within the window.

Change-Id: Iccba9fb307f98a4fc145402ecd0a38f3d75b3253
Merge "Report queue window in status JSON."