WIP, redesigning forecast.py;

[enzbus]

using composition to break forecasters into elementary ones; will add logic to manage "workspace" in BaseForecast so each is evaled only once; need to untangle EMW-MW logic which was too complicated; hopefully will make more advanced forecasters easier to develop; will also merge cache.py into BaseForecast and remove related logic from simulator.py in this branch and merge for 1.4.0