Cache codes from API, only fetch new ones after a certain amount of time #13

To help with server load from the API provided by shift.orcicorn.com, we should cache the available codes and only request new ones if the cache is old.

This occurs at 00:02, 06:02, 12:02 and 18:02 server-time ( New York, USA )

On redeem, we want to store the result. Time should probably be based on the meta.generated field. On the next redeem request, check if the current time in New York, USA is > 1 hour from the meta.generated. If it is, send the request. If not, use the cached codes.