mediawiki.page.image.pagination: Cache last-loaded pages

I often find myself switching back-and-forth between the few pages I
last looked at. Let's cache their information to avoid downloading it
again and again.

I've only implemented a count-based limit on the queue (no more than
10 entries) and no time-based limit (entries never expire). I don't
think one is necessary, but that might be due to my laziness…

Change-Id: I5873946e3e3b37a8951c1ac84e3e1a206b9300d1
Merge "mediawiki.page.image.pagination: Cache last-loaded pages"