#2 Implement configurable Value Object Cache to reduce NextBus call overhead

[Jim Doyle]

Implement and test the stackable VO Cache. The cache will provide configurable age-based expiration policy such that more durable elements (i.e. routes, agencies) are retained for
longer periods than the more volatile elements such as Vehicle Location and Prediction.

The Cache is necessary to reduce overhead on called to NextBus and provide a means a scaleable, high-volume local application service (such as for the MBTA Boston area).