First pass: cache manager uses SmartStore

Not sure that this is ready to merge into unstable yet, as it's all untested code.  It builds though. :)  This is a good cutoff for initial review.  Updates here are switching cache manager off of the file system, and onto SmartStore as the backing persisted cache.
I simplified the data model, so that there's only one index spec: the cache key.  The cache type is the soup/table itself.  The data is not indexed.