Do clean-up edit of Cart Model

After writing the cache features for Cart, the code needed a final code to smooth things out.

More properties were made to eliminate the 14 specific mentions of cache configurations.

The two variants of cache name constructors were merged and renamed

Doc blocks were added where missing

cart-count memory cache was config'd in bootstrap
Creation of a Purchases Component

Many Cart Controller methods will be needed on every page.  The Purcahses Component will serve as a collection point.
Debugged the changeover to Purchase Component from Cart Controller
oops. don't leve debugs in the core
move basic setup pieces to component