Revamped caching.  FishService now has a Level 1 (memory) and Level 2
(memcache) cache.  FishesServlet has a Level 1 (memory) cache for the
served JSON effectively creating a cache for the serialized version of
the data.  Cache invalidation now also works correctly.

Overall latency should improve - even immediately after a server push
due to the Level 2 cache in FishService.