Previously, state was extensively persisted in the cache. This
large-scale rewrite uses the cache only to persist changes to the
catalog file when it is read-only. State is now conveyed through the url
structure and through query string arguments.
The primary downside to this new approach is that there's no explicit
way of purging a cached catalog from memory, or refreshing it from
what's on disk. The user is forced (untransparently!) to wait until
the cached file falls out of the cache (untransparently!), which
is currently 24 hours after the last save (or after if the session
ends). Addressing this would require some design considerations,
and probably some new text that would require its own translation.
