When Viewing a Space Version, we should show appropriate Conversations

(User Story, Investigate , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
History, Conversations
Summary: Currently, we simply don't show Conversations when viewing History. We should show the state of the Conversations for the Thing at this Timestamp.
In principle this isn't insanely hard. View State currently includes a pseudo-parameter which is the Version; we would need to add another which is the Timestamp we're viewing. We would open up the read side of the Conversations API; if we try to fetch the Conversations for a Thing and the Version Timestamp is set, we would use Persistence Query to fetch the state of the Conversations at that point. It might not even need / want a separate Actor -- simply creating an object that loads the stream to the specified time and returns the ThingConversations would suffice, I believe.
Note that the edit side of the Conversations API would need to reject in this case.
In theory, this would be very nice to have. In practice, since Conversations are nearly-immutable and timestamped, it isn't terribly crucial.