Remove all the Lotus stuff
Implement Repository Pattern using Sequel
Memoize Order#contents
Switch PromotionHandler::Cart#activate to PromotionHandler::Cart.activate

For a couple of reasons:

1) It makes it easier to stub Spree::PromotionHandler::Cart.promotions in tests that shouldn't call out to the database.
2) There's no point having it initialize a *whole new object* which defines one single method. Instead, let's use the object that's already 'initialized': the class.