Simplify SPOState messaging #471
Description
SPOState holds a stake address map (if store is configured) and subscribes to all the topics needed to update it, which really complicates the message flow in that area. It would be nice if this was pulled out into a separate historical module, and/or queried AccountsState for whatever it is that it needs.
** Definition of done
Acropolis works as before - including the /pool REST interfaces which this impacts - but the message graph and SPOState itself is simpler.