Added file cache.py
Added file cache.py

That file should have been added in 443f3c6b5f95425955328fd7d59296cbcb329ba4

GeographicaGS/moocng,GeographicaGS/moocng,GeographicaGS/moocng,GeographicaGS/moocng,OpenMOOC/moocng,OpenMOOC/moocng