EconomicSim, CitiesData

Built out placeholders for EconomicSim and CitiesData. Beefed up WorldState. Added another worker thread for WorldState to run in (CVServer now manages two; one for world state and the other for the session manager handling client connections).

I realized I hadn't really thought a part of my design all the way through. When you bought or sold a good, the idea was you'd just consult static data to find out how much the good was (which would be the same between server and client, because that state is all server authoritative). But my design for good prices is time sensitive (and potentially sensitive to other variables). The client needs a snapshot of state from the server that it will know is good for a certain amount of time, and then that needs to get threaded through to all PlayerState-modifying requests. To do tomorrow.

I'm really hoping to return to Unity soon--it would be nice to start hooking up all this backend to something graphical.